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Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback

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  Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback "Luis R. Rodriguez" <mcgrof@kernel.org> - 2017-05-25 00:40 +0200
    Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback Andy Lutomirski <luto@kernel.org> - 2017-05-25 06:20 +0200
      Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback "Fuzzey, Martin" <mfuzzey@parkeon.com> - 2017-05-25 10:30 +0200
        Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback ebiederm@xmission.com (Eric W. Biederman) - 2017-05-26 13:20 +0200
          Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on  fallback "Luis R. Rodriguez" <mcgrof@kernel.org> - 2017-05-26 21:50 +0200
            Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback Dmitry Torokhov <dmitry.torokhov@gmail.com> - 2017-05-27 03:30 +0200
              Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on  fallback Dmitry Torokhov <dmitry.torokhov@gmail.com> - 2017-05-27 03:30 +0200
                Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on  fallback "Luis R. Rodriguez" <mcgrof@kernel.org> - 2017-06-05 22:30 +0200
                  Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on  fallback Martin Fuzzey <mfuzzey@parkeon.com> - 2017-06-06 11:10 +0200
                    Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on  fallback "Luis R. Rodriguez" <mcgrof@kernel.org> - 2017-06-06 18:40 +0200
                      Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on  fallback "Luis R. Rodriguez" <mcgrof@kernel.org> - 2017-06-06 20:00 +0200
                  Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on  fallback Alan Cox <alan@linux.intel.com> - 2017-06-06 17:00 +0200
                    Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on  fallback "Luis R. Rodriguez" <mcgrof@kernel.org> - 2017-06-06 18:50 +0200
                      Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on  fallback "Luis R. Rodriguez" <mcgrof@kernel.org> - 2017-06-06 20:00 +0200
                      Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on  fallback Theodore Ts'o <tytso@mit.edu> - 2017-06-07 00:20 +0200
                        Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on  fallback "Luis R. Rodriguez" <mcgrof@kernel.org> - 2017-06-07 02:30 +0200
                          Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback Andy Lutomirski <luto@kernel.org> - 2017-06-07 07:00 +0200
                            Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on  fallback Dmitry Torokhov <dmitry.torokhov@gmail.com> - 2017-06-07 08:30 +0200
                              Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on  fallback Alan Cox <alan@linux.intel.com> - 2017-06-07 14:30 +0200
              Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback "Luis R. Rodriguez" <mcgrof@kernel.org> - 2017-05-27 03:30 +0200
        Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on  fallback "Luis R. Rodriguez" <mcgrof@kernel.org> - 2017-05-26 21:50 +0200
          Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on  fallback "Luis R. Rodriguez" <mcgrof@kernel.org> - 2017-05-27 03:30 +0200
          Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback "Fuzzey, Martin" <mfuzzey@parkeon.com> - 2017-05-27 03:50 +0200

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#1650006 — Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback

On Wed, May 24, 2017 at 3:00 PM, Andy Lutomirski <luto@kernel.org> wrote:
> On Wed, May 24, 2017 at 2:40 PM, Luis R. Rodriguez <mcgrof@kernel.org> wrote:
>> From: Martin Fuzzey <mfuzzey@parkeon.com>
>>
>> Commit 0cb64249ca500 ("firmware_loader: abort request if wait_for_completion
>> is interrupted") added via 4.0 added support to abort the fallback mechanism
>> when a signal was detected and wait_for_completion_interruptible() returned
>> -ERESTARTSYS. Although the abort was effective we were unfortunately never
>> really propagating this error though and as such userspace could not know
>> why the abort happened.
>
> Can you give a simple example of what's going on and why it matters?
>
> ERESTARTSYS and friends are highly magical, and I'm not convinced that
> allowing _request_firmware_load to return -ERESTARTSYS is actually a
> good idea.  What if there are system calls that can't handle this
> style of restart that start being restarted as a result?

This seems to be a linux-api question, so Cc'ing them and Michael.

For those not familiar it is worth explaining first the user interface.

This describes the fallback mechanism of the Linux firmware API if
direct filesystem lookup fails. Although most distros disable this
stuff today some distros (Android) seem to be always relying on it
today. Other than Android, since most distros have the forced fallback
mechanism off but *enable* requests to require it, only 2 upstream
drivers do this, so on other distros we only have 2 drivers which
typically require the the fallback mechanism.

The exposed user interface here is we enable a knob through sysfs to
enable userspace to write a file as a fallback mechanism then, and we
expect to get woken up today when userspace finds the needed file and
then writes the file to the sysfs knob. We wait for userspace using
swait_event_interruptible_timeout(). While we wait we can get a
-ERESTARTSYS since swait_event_interruptible_timeout() uses
__swait_event_interruptible_timeout() under the hood and this in turn
___swait_event() which can prepare_to_swait_event() which can return
-ERESTARTSYS on signal_pending_state().

The issue discovered was that Android could issue SIGCHLD and the
waiter gets a signal but the reason for the exact reason for the
failure is not propagated. The proposed patch propagates -ERESTARTSYS
when that is returned on signal_pending_state() as we wait.

So linux-api folks please speak up.

 Luis

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#1650163

On Wed, May 24, 2017 at 3:38 PM, Luis R. Rodriguez <mcgrof@kernel.org> wrote:
> On Wed, May 24, 2017 at 3:00 PM, Andy Lutomirski <luto@kernel.org> wrote:
>> On Wed, May 24, 2017 at 2:40 PM, Luis R. Rodriguez <mcgrof@kernel.org> wrote:
>>> From: Martin Fuzzey <mfuzzey@parkeon.com>
>>>
>>> Commit 0cb64249ca500 ("firmware_loader: abort request if wait_for_completion
>>> is interrupted") added via 4.0 added support to abort the fallback mechanism
>>> when a signal was detected and wait_for_completion_interruptible() returned
>>> -ERESTARTSYS. Although the abort was effective we were unfortunately never
>>> really propagating this error though and as such userspace could not know
>>> why the abort happened.
>>
>> Can you give a simple example of what's going on and why it matters?
>>
>> ERESTARTSYS and friends are highly magical, and I'm not convinced that
>> allowing _request_firmware_load to return -ERESTARTSYS is actually a
>> good idea.  What if there are system calls that can't handle this
>> style of restart that start being restarted as a result?
>
> This seems to be a linux-api question, so Cc'ing them and Michael.
>
> For those not familiar it is worth explaining first the user interface.
>
> This describes the fallback mechanism of the Linux firmware API if
> direct filesystem lookup fails.

...

> While we wait we can get a
> -ERESTARTSYS since swait_event_interruptible_timeout() uses
> __swait_event_interruptible_timeout() under the hood and this in turn
> ___swait_event() which can prepare_to_swait_event() which can return
> -ERESTARTSYS on signal_pending_state().

This is too much kernel detail and too little ABI detail.

User code does some syscall.  Kernel requests firmware and that
request gets interrupted.  What syscall is this?  read(2)?  open(2)?
Something else?

mutex_lock_interruptible() returns -EINTR if interrupted.  It seems
odd to be that requesting firmware would be different.

>
> The issue discovered was that Android could issue SIGCHLD and the
> waiter gets a signal but the reason for the exact reason for the
> failure is not propagated. The proposed patch propagates -ERESTARTSYS
> when that is returned on signal_pending_state() as we wait.

Maybe SIGCHLD shouldn't interrupt firmware loading?

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#1650299

On 25 May 2017 at 06:13, Andy Lutomirski <luto@kernel.org> wrote:
>>>
>>> Can you give a simple example of what's going on and why it matters?
>>>


Here is the use case in which I ran into this problem.

I have a driver which does request_firmware() when a write() is done
to a sysfs file.

The write() was being done by an android init script (with the init
interpreter "write" command).
init, of course, forks lots of processes and some of the children die.

So the scenario was the following:

1) Android init calls write() on the sysfs file
2) The sysfs .store() callback registered by a driver is called
3) The driver calls request_firmware()
4) request_firmware() sends the firmware load request to userspace and
calls wait_for_completion_interruptible()
5) A child dies and raises SIGCHLD
6) wait_for_completion_interruptible() returns -ERESTARTSYS due to the signal
7) request_firmware() [before this patch] translated that to -EAGAIN
8) The driver (in my case) ignored this [because the firmware was not
critical - it was for checking if a microcontroler was up to date]
(but it could have returned it to userspace, same problem)

The point being that, due to a signal (SIGCHLD) which has nothing to
do with the firmware loading process, the firmware load was not done.
Also EAGAIN is the same error used if the load request times out so it
was impossible to distinguish the two cases.

ERESTARTSYS is an internal error and is not returned to userspace.
Instead it is handled by the linux syscall machinery which, after
processing the signal either restarts (transpently to userspace) the
syscall or returns EINTR to userspace (depending if the signal handler
users SA_RESTART - see man 7 signal)


With this patch here is what happens:

1) Android init calls write() on the sysfs file
2) The sysfs .store() callback registered by a driver is called
3) The driver calls request_firmware()
4) request_firmware() sends the firmware load request to userspace and
calls wait_for_completion_interruptible()
5) A child dies and raises SIGCHLD
6) wait_for_completion_interruptible() returns -ERESTARTSYS due to the signal
7) request_firmware() [with this patch] returns -ERESTARTSYS
8) The driver returns -ERSTARTSYS from its sysfs .store method
9) The system call machinery invokes the signal handler
10) The signal handler does its stuff
11) Because SA_RESTART was set the system call is restarted (calling
the sysfs .store) and we try it all again from step 2

Note that, on the the userspace side  write() is only called once (the
restart is transparent to userspace which is oblivious to all this)
The kernel side write() (which calls .store() is called multiple times
(so that code does need to know about this)


>>> ERESTARTSYS and friends are highly magical, and I'm not convinced that
>>> allowing _request_firmware_load to return -ERESTARTSYS is actually a
>>> good idea.  What if there are system calls that can't handle this
>>> style of restart that start being restarted as a result?
>>

If the caller is unable to restart (for example if the driver's
.store() callback had already done lots of stuff that couldn't be
undone) it is free to translate -ERSTARTSYS to -EINTR before
returning.
But request_frimware() can't know about that.


>>> Maybe SIGCHLD shouldn't interrupt firmware loading?

I don't think there's a way of doing that without disabling all
signals (ie using the non interruptible wait variants).
It used to be that way (which is why I only ran into this after
updating from an ancient 3.16 kernel to a slightly less ancient 4.4)
But there are valid reasons for wanting to be able to interrupt
firmware loading (like being able to kill the userspace helper)

Hope this explains it better,

Regads,

Martin

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#1651313

"Fuzzey, Martin" <mfuzzey@parkeon.com> writes:

> On 25 May 2017 at 06:13, Andy Lutomirski <luto@kernel.org> wrote:
>>>>
>>>> Can you give a simple example of what's going on and why it matters?
>>>>
>
>
> Here is the use case in which I ran into this problem.
>
> I have a driver which does request_firmware() when a write() is done
> to a sysfs file.
>
> The write() was being done by an android init script (with the init
> interpreter "write" command).
> init, of course, forks lots of processes and some of the children die.
>
> So the scenario was the following:
>
> 1) Android init calls write() on the sysfs file
> 2) The sysfs .store() callback registered by a driver is called
> 3) The driver calls request_firmware()
> 4) request_firmware() sends the firmware load request to userspace and
> calls wait_for_completion_interruptible()
> 5) A child dies and raises SIGCHLD
> 6) wait_for_completion_interruptible() returns -ERESTARTSYS due to the signal
> 7) request_firmware() [before this patch] translated that to -EAGAIN
> 8) The driver (in my case) ignored this [because the firmware was not
> critical - it was for checking if a microcontroler was up to date]
> (but it could have returned it to userspace, same problem)
>
> The point being that, due to a signal (SIGCHLD) which has nothing to
> do with the firmware loading process, the firmware load was not done.
> Also EAGAIN is the same error used if the load request times out so it
> was impossible to distinguish the two cases.
>
> ERESTARTSYS is an internal error and is not returned to userspace.
> Instead it is handled by the linux syscall machinery which, after
> processing the signal either restarts (transpently to userspace) the
> syscall or returns EINTR to userspace (depending if the signal handler
> users SA_RESTART - see man 7 signal)
>
>
> With this patch here is what happens:
>
> 1) Android init calls write() on the sysfs file
> 2) The sysfs .store() callback registered by a driver is called
> 3) The driver calls request_firmware()
> 4) request_firmware() sends the firmware load request to userspace and
> calls wait_for_completion_interruptible()
> 5) A child dies and raises SIGCHLD
> 6) wait_for_completion_interruptible() returns -ERESTARTSYS due to the signal
> 7) request_firmware() [with this patch] returns -ERESTARTSYS
> 8) The driver returns -ERSTARTSYS from its sysfs .store method
> 9) The system call machinery invokes the signal handler
> 10) The signal handler does its stuff
> 11) Because SA_RESTART was set the system call is restarted (calling
> the sysfs .store) and we try it all again from step 2
>
> Note that, on the the userspace side  write() is only called once (the
> restart is transparent to userspace which is oblivious to all this)
> The kernel side write() (which calls .store() is called multiple times
> (so that code does need to know about this)
>
>
>>>> ERESTARTSYS and friends are highly magical, and I'm not convinced that
>>>> allowing _request_firmware_load to return -ERESTARTSYS is actually a
>>>> good idea.  What if there are system calls that can't handle this
>>>> style of restart that start being restarted as a result?
>>>
>
> If the caller is unable to restart (for example if the driver's
> .store() callback had already done lots of stuff that couldn't be
> undone) it is free to translate -ERSTARTSYS to -EINTR before
> returning.
> But request_frimware() can't know about that.
>
>
>>>> Maybe SIGCHLD shouldn't interrupt firmware loading?
>
> I don't think there's a way of doing that without disabling all
> signals (ie using the non interruptible wait variants).
> It used to be that way (which is why I only ran into this after
> updating from an ancient 3.16 kernel to a slightly less ancient 4.4)
> But there are valid reasons for wanting to be able to interrupt
> firmware loading (like being able to kill the userspace helper)

Perhaps simply using a killable wait and not a fully interruptible
wait would be better?

It sounds like the code really is not prepared for an truly
interruptible wait here.

Eric

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#1651591 — Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback

On Fri, May 26, 2017 at 06:09:29AM -0500, Eric W. Biederman wrote:
> "Fuzzey, Martin" <mfuzzey@parkeon.com> writes:
> >>>> Maybe SIGCHLD shouldn't interrupt firmware loading?
> >
> > I don't think there's a way of doing that without disabling all
> > signals (ie using the non interruptible wait variants).
> > It used to be that way (which is why I only ran into this after
> > updating from an ancient 3.16 kernel to a slightly less ancient 4.4)
> > But there are valid reasons for wanting to be able to interrupt
> > firmware loading (like being able to kill the userspace helper)
> 
> Perhaps simply using a killable wait and not a fully interruptible
> wait would be better?

What do you mean by a killable wait BTW?

ret = swait_event_interruptible_timeout() is being used right now.

The problem is we have:

        if (ret != 0 && fw_st->status == FW_STATUS_ABORTED)                     
                return -ENOENT;                                                 
        if (!ret)                                                               
                return -ETIMEDOUT;                                              
                                                                                
        return ret < 0 ? ret : 0;  

The (!ret) return -ETIMEDOUT ensures that if there was no time left
then we know we ran out of time.

The ret < 0 ? ret makes sure we send any errors
swait_event_interruptible_timeout() sent.

But the caller of this code has:

        if (fw_state_is_aborted(&buf->fw_st))                                   
                retval = -EAGAIN;                                               
        else if (buf->is_paged_buf && !buf->data)                               
                retval = -ENOMEM; 

And this retval is used. so we mask all errors with -EAGAIN.

So Martin is asking us to let us send -ERESTARTSYS back down to drivers.
These potentially could send back down to probe, and so finit_module()
could get this.

Another use case is a custom syfs knob which triggers a request_firmware(),
in such case this is a simple write(), but Anroid is configured to retry
if -ERESTARTSYS so I gather it will *retry* writing again to this file
if -ERESTARTSYS was sent and therefore triggering another firmware request.

> It sounds like the code really is not prepared for an truly
> interruptible wait here.

Can you clarify what you mean?

  Luis

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#1651623

On Fri, May 26, 2017 at 12:46 PM, Luis R. Rodriguez <mcgrof@kernel.org> wrote:
> On Fri, May 26, 2017 at 06:09:29AM -0500, Eric W. Biederman wrote:
>> "Fuzzey, Martin" <mfuzzey@parkeon.com> writes:
>> >>>> Maybe SIGCHLD shouldn't interrupt firmware loading?
>> >
>> > I don't think there's a way of doing that without disabling all
>> > signals (ie using the non interruptible wait variants).
>> > It used to be that way (which is why I only ran into this after
>> > updating from an ancient 3.16 kernel to a slightly less ancient 4.4)
>> > But there are valid reasons for wanting to be able to interrupt
>> > firmware loading (like being able to kill the userspace helper)
>>
>> Perhaps simply using a killable wait and not a fully interruptible
>> wait would be better?
>
> What do you mean by a killable wait BTW?

https://lwn.net/Articles/288056/

I think only interrupting firmware loading with fatal signals would
make a lot of sense.

>
> ret = swait_event_interruptible_timeout() is being used right now.

It looks like we are missing swait_event_killable*(), but I do not
think it would be hard to add.

-- 
Dmitry

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#1651634 — Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback

On Fri, May 26, 2017 at 02:32:31PM -0700, Luis R. Rodriguez wrote:
> On Fri, May 26, 2017 at 2:26 PM, Dmitry Torokhov
> <dmitry.torokhov@gmail.com> wrote:
> > On Fri, May 26, 2017 at 12:46 PM, Luis R. Rodriguez <mcgrof@kernel.org> wrote:
> >> On Fri, May 26, 2017 at 06:09:29AM -0500, Eric W. Biederman wrote:
> >>> "Fuzzey, Martin" <mfuzzey@parkeon.com> writes:
> >>> >>>> Maybe SIGCHLD shouldn't interrupt firmware loading?
> >>> >
> >>> > I don't think there's a way of doing that without disabling all
> >>> > signals (ie using the non interruptible wait variants).
> >>> > It used to be that way (which is why I only ran into this after
> >>> > updating from an ancient 3.16 kernel to a slightly less ancient 4.4)
> >>> > But there are valid reasons for wanting to be able to interrupt
> >>> > firmware loading (like being able to kill the userspace helper)
> >>>
> >>> Perhaps simply using a killable wait and not a fully interruptible
> >>> wait would be better?
> >>
> >> What do you mean by a killable wait BTW?
> >
> > https://lwn.net/Articles/288056/
> >
> > I think only interrupting firmware loading with fatal signals would
> > make a lot of sense.
> >
> >>
> >> ret = swait_event_interruptible_timeout() is being used right now.
> >
> > It looks like we are missing swait_event_killable*(), but I do not
> > think it would be hard to add.
> 
> What should we do for stable ? Is this a *stable* issue ?

I think it is, as you have users complaining about behavior. I do not
think we need to make their lives harder than needed by requiring
handling signals.

I do not see why we could not introduce wait_event_killable_timeout()
and swait_event_killable_timeout() into -stables.

Thanks.

-- 
Dmitry

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#1658130 — Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback

On Fri, May 26, 2017 at 02:55:18PM -0700, Dmitry Torokhov wrote:
> On Fri, May 26, 2017 at 02:32:31PM -0700, Luis R. Rodriguez wrote:
> > On Fri, May 26, 2017 at 2:26 PM, Dmitry Torokhov
> > <dmitry.torokhov@gmail.com> wrote:
> > > On Fri, May 26, 2017 at 12:46 PM, Luis R. Rodriguez <mcgrof@kernel.org> wrote:
> > >> On Fri, May 26, 2017 at 06:09:29AM -0500, Eric W. Biederman wrote:
> > >>> "Fuzzey, Martin" <mfuzzey@parkeon.com> writes:
> > >>> >>>> Maybe SIGCHLD shouldn't interrupt firmware loading?
> > >>> >
> > >>> > I don't think there's a way of doing that without disabling all
> > >>> > signals (ie using the non interruptible wait variants).
> > >>> > It used to be that way (which is why I only ran into this after
> > >>> > updating from an ancient 3.16 kernel to a slightly less ancient 4.4)
> > >>> > But there are valid reasons for wanting to be able to interrupt
> > >>> > firmware loading (like being able to kill the userspace helper)
> > >>>
> > >>> Perhaps simply using a killable wait and not a fully interruptible
> > >>> wait would be better?
> > >>
> > >> What do you mean by a killable wait BTW?
> > >
> > > https://lwn.net/Articles/288056/

Read it thanks ! As per this it states, "Kernel code which uses interruptible
sleeps must always check to see whether it woke up as a result of a signal,
and, if so, clean up whatever it was doing and return -EINTR back to user
space." -- but also on the same article it quotes Alan Cox as having noted
"Unix tradition (and thus almost all applications) believe file store writes to
be non signal interruptible. It would not be safe or practical to change that
guarantee."

For these two reasons then it would seem best we do two things actually:

1) return -EINTR instead of -EAGAIN when we detect swait_event_interruptible_timeout()
got interrupted by a signal (it returns -ERESTARTSYS)
2) Do as you note below and add wait_event_killable_timeout()

> > > I think only interrupting firmware loading with fatal signals would
> > > make a lot of sense.
> > >
> > >>
> > >> ret = swait_event_interruptible_timeout() is being used right now.
> > >
> > > It looks like we are missing swait_event_killable*(), but I do not
> > > think it would be hard to add.
> > 
> > What should we do for stable ? Is this a *stable* issue ?
> 
> I think it is, as you have users complaining about behavior. I do not
> think we need to make their lives harder than needed by requiring
> handling signals.

Makes sense, specially given the long tradition, it would breaking a long
tradition. Even though in this case we are dealing with sysfs files it
should be no different.

> I do not see why we could not introduce wait_event_killable_timeout()
> and swait_event_killable_timeout() into -stables.

After seeing how simple it is to do so I tend to agree. Greg, Peter,
what are your thoughts ?

Martin Fuzzey can you test this patch as an alternative to your issue ?

diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
index b9f907eedbf7..70fc42e5e0da 100644
--- a/drivers/base/firmware_class.c
+++ b/drivers/base/firmware_class.c
@@ -131,7 +131,7 @@ static int __fw_state_wait_common(struct fw_state *fw_st, long timeout)
 {
 	long ret;
 
-	ret = swait_event_interruptible_timeout(fw_st->wq,
+	ret = swait_event_killable_timeout(fw_st->wq,
 				__fw_state_is_done(READ_ONCE(fw_st->status)),
 				timeout);
 	if (ret != 0 && fw_st->status == FW_STATUS_ABORTED)
diff --git a/include/linux/swait.h b/include/linux/swait.h
index c1f9c62a8a50..9c5ca2898b2f 100644
--- a/include/linux/swait.h
+++ b/include/linux/swait.h
@@ -169,4 +169,29 @@ do {									\
 	__ret;								\
 })
 
+#define __swait_event_killable(wq, condition)				\
+	(void)___swait_event(wq, condition, TASK_KILLABLE, 0, schedule())
+
+#define swait_event_killable(wq, condition)				\
+({									\
+	int __ret = 0;							\
+	if (!(condition))						\
+		__ret = __swait_event_killable(wq, condition);		\
+	__ret;								\
+})
+
+#define __swait_event_killable_timeout(wq, condition, timeout)		\
+	___swait_event(wq, ___wait_cond_timeout(condition),		\
+		      TASK_INTERRUPTIBLE, timeout,			\
+		      __ret = schedule_timeout(__ret))
+
+#define swait_event_killable_timeout(wq, condition, timeout)		\
+({									\
+	long __ret = timeout;						\
+	if (!___wait_cond_timeout(condition))				\
+		__ret = __swait_event_killable_timeout(wq,		\
+						condition, timeout);	\
+	__ret;								\
+})
+
 #endif /* _LINUX_SWAIT_H */

  Luis

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#1658504 — Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback

On 05/06/17 22:24, Luis R. Rodriguez wrote:
>
>
> For these two reasons then it would seem best we do two things actually:
>
> 1) return -EINTR instead of -EAGAIN when we detect swait_event_interruptible_timeout()
> got interrupted by a signal (it returns -ERESTARTSYS)


I disagree. That would force userspace to handle the signal rather than 
having the kernel retry.

 From Documentation/DocBook/kernel-hacking.tmpl:

    After you slept you should check if a signal occurred: the
    Unix/Linux way of handling signals is to temporarily exit the
    system call with the <constant>-ERESTARTSYS</constant> error.  The
    system call entry code will switch back to user context, process
    the signal handler and then your system call will be restarted
    (unless the user disabled that).  So you should be prepared to
    process the restart, e.g. if you're in the middle of manipulating
    some data structure.



> 2) Do as you note below and add wait_event_killable_timeout()

Hum,
I do think that would be better but, (please correct me if I'm wrong) 
the _killable_ variants only allow
SIGKILL  (and not SIGINT).

0cb64249ca "firmware_loader: abort request if wait_for_completion is 
interrupted"

specifically mentrions ctrl-c (SIGINT) in the commit message so that 
would no longer work.

Myself I think having to use kill -9 to interrupt firmware loading by a 
usespace helper is OK but others may disagree.

> I do not see why we could not introduce wait_event_killable_timeout()
> and swait_event_killable_timeout() into -stables.
> After seeing how simple it is to do so I tend to agree. Greg, Peter,
> what are your thoughts ?
>
> Martin Fuzzey can you test this patch as an alternative to your issue ?
>
> diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
> index b9f907eedbf7..70fc42e5e0da 100644
> --- a/drivers/base/firmware_class.c
> +++ b/drivers/base/firmware_class.c
> @@ -131,7 +131,7 @@ static int __fw_state_wait_common(struct fw_state *fw_st, long timeout)
>   {
>   	long ret;
>   
> -	ret = swait_event_interruptible_timeout(fw_st->wq,
> +	ret = swait_event_killable_timeout(fw_st->wq,
>   				__fw_state_is_done(READ_ONCE(fw_st->status)),
>   				timeout);
>   	if (ret != 0 && fw_st->status == FW_STATUS_ABORTED)
> diff --git a/include/linux/swait.h b/include/linux/swait.h
> index c1f9c62a8a50..9c5ca2898b2f 100644
> --- a/include/linux/swait.h
> +++ b/include/linux/swait.h
> @@ -169,4 +169,29 @@ do {									\
>   	__ret;								\
>   })
>   
> +#define __swait_event_killable(wq, condition)				\
> +	(void)___swait_event(wq, condition, TASK_KILLABLE, 0, schedule())
> +
> +#define swait_event_killable(wq, condition)				\
> +({									\
> +	int __ret = 0;							\
> +	if (!(condition))						\
> +		__ret = __swait_event_killable(wq, condition);		\
> +	__ret;								\
> +})
> +
> +#define __swait_event_killable_timeout(wq, condition, timeout)		\
> +	___swait_event(wq, ___wait_cond_timeout(condition),		\
> +		      TASK_INTERRUPTIBLE, timeout,			\
> +		      __ret = schedule_timeout(__ret))
> +

Should be TASK_KILLABLE above

> +#define swait_event_killable_timeout(wq, condition, timeout)		\
> +({									\
> +	long __ret = timeout;						\
> +	if (!___wait_cond_timeout(condition))				\
> +		__ret = __swait_event_killable_timeout(wq,		\
> +						condition, timeout);	\
> +	__ret;								\
> +})
> +
>   #endif /* _LINUX_SWAIT_H */
>
>    Luis

After replacing TASK_INTERRUPTIBLE with TASK_KILLABLE above it works for me.


Regards,

Martin

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#1658934 — Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback

Adding fsdevel for review on the correct semantics of handling signals on
write(), in this case a sysfs write which triggered a sync request firmware
call and what the firmware API should return in such case of a signal (I gather
this should be -EINTR and not -ERESTARTSYS). Also whether or not SIGINT should
be followed or if only allowing SIGKILL is fine (fine by me, but it would
change old behaviour).

Hoping between fsdevel and linux-api folks we can hash this out.

On Tue, Jun 06, 2017 at 11:04:37AM +0200, Martin Fuzzey wrote:
> On 05/06/17 22:24, Luis R. Rodriguez wrote:
> > 
> > 
> > For these two reasons then it would seem best we do two things actually:
> > 
> > 1) return -EINTR instead of -EAGAIN when we detect swait_event_interruptible_timeout()
> > got interrupted by a signal (it returns -ERESTARTSYS)
> 
> 
> I disagree. That would force userspace to handle the signal rather than
> having the kernel retry.
> 
> From Documentation/DocBook/kernel-hacking.tmpl:
> 
>    After you slept you should check if a signal occurred: the
>    Unix/Linux way of handling signals is to temporarily exit the
>    system call with the <constant>-ERESTARTSYS</constant> error.  The
>    system call entry code will switch back to user context, process
>    the signal handler and then your system call will be restarted
>    (unless the user disabled that).  So you should be prepared to
>    process the restart, e.g. if you're in the middle of manipulating
>    some data structure.

This applies but you are missing my point that the LWN article [0] I referred
to also stated "Kernel code which uses interruptible sleeps must always check
to see whether it woke up as a result of a signal, and, if so, clean up
whatever it was doing and return -EINTR back to user space." -- I realize there
may be contradiction with above documentation -- this perhaps can be clarified
with fsdevel folks *but* regardless of that the same article notes Alan Cox
explains that "Unix tradition (and thus almost all applications) believe file
store writes to be non signal interruptible. It would not be safe or practical
to change that guarantee." So for this reason alone there does seem to be an
exemption to the above documentation worth noting for file store writes, and
the patch which you tested below *moves* the sysfs write op for firmware in
that direction by adding a new killable swait.

[0] https://lwn.net/Articles/288056/                                                                                                                                          
                                                                                                                                                                                
> > 2) Do as you note below and add wait_event_killable_timeout()
> 
> Hum,  I do think that would be better but, (please correct me if I'm wrong)
> the _killable_ variants only allow SIGKILL  (and not SIGINT).

That seems correct given a TASK_KILLABLE is also TASK_UNINTERRUPTIBLE.

> 0cb64249ca "firmware_loader: abort request if wait_for_completion is
> interrupted"
> 
> specifically mentrions ctrl-c (SIGINT) in the commit message so that would
> no longer work.

Great point, but it *also* allowed SIGKILL, so I do feel the goal was also to
allow it to be killable. I'm afraid that patch probably did not get proper
review from sufficient folks and its worth now asking ourselves what we'd like
to do.  I'm fine with letting go of SIGINT for firmware sysfs calls for the
sake of keeping with the long standing unix tradition on write, given we *still
have SIGKILL*.

> Myself I think having to use kill -9 to interrupt firmware loading by a
> usespace helper is OK but others may disagree.

Its why I added fsdevel as well. This is really a semantics and uapi question.
Between fsdevel and linux-api folks I would hope we can come to a sensible
resolution.

> > I do not see why we could not introduce wait_event_killable_timeout()
> > and swait_event_killable_timeout() into -stables.
> > After seeing how simple it is to do so I tend to agree. Greg, Peter,
> > what are your thoughts ?
> > 
> > Martin Fuzzey can you test this patch as an alternative to your issue ?
> > 
> > diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
> > index b9f907eedbf7..70fc42e5e0da 100644
> > --- a/drivers/base/firmware_class.c
> > +++ b/drivers/base/firmware_class.c
> > @@ -131,7 +131,7 @@ static int __fw_state_wait_common(struct fw_state *fw_st, long timeout)
> >   {
> >   	long ret;
> > -	ret = swait_event_interruptible_timeout(fw_st->wq,
> > +	ret = swait_event_killable_timeout(fw_st->wq,
> >   				__fw_state_is_done(READ_ONCE(fw_st->status)),
> >   				timeout);
> >   	if (ret != 0 && fw_st->status == FW_STATUS_ABORTED)
> > diff --git a/include/linux/swait.h b/include/linux/swait.h
> > index c1f9c62a8a50..9c5ca2898b2f 100644
> > --- a/include/linux/swait.h
> > +++ b/include/linux/swait.h
> > @@ -169,4 +169,29 @@ do {									\
> >   	__ret;								\
> >   })
> > +#define __swait_event_killable(wq, condition)				\
> > +	(void)___swait_event(wq, condition, TASK_KILLABLE, 0, schedule())
> > +
> > +#define swait_event_killable(wq, condition)				\
> > +({									\
> > +	int __ret = 0;							\
> > +	if (!(condition))						\
> > +		__ret = __swait_event_killable(wq, condition);		\
> > +	__ret;								\
> > +})
> > +
> > +#define __swait_event_killable_timeout(wq, condition, timeout)		\
> > +	___swait_event(wq, ___wait_cond_timeout(condition),		\
> > +		      TASK_INTERRUPTIBLE, timeout,			\
> > +		      __ret = schedule_timeout(__ret))
> > +
> 
> Should be TASK_KILLABLE above

Oops yes sorry.

> > +#define swait_event_killable_timeout(wq, condition, timeout)		\
> > +({									\
> > +	long __ret = timeout;						\
> > +	if (!___wait_cond_timeout(condition))				\
> > +		__ret = __swait_event_killable_timeout(wq,		\
> > +						condition, timeout);	\
> > +	__ret;								\
> > +})
> > +
> >   #endif /* _LINUX_SWAIT_H */
> > 
> >    Luis
> 
> After replacing TASK_INTERRUPTIBLE with TASK_KILLABLE above it works for me.

Great, thanks for testing.

  Luis

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#1658999 — Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback

Used wrong alias for fsdevel now, its linux-fsdevel ...

  Luis

On Tue, Jun 06, 2017 at 06:34:01PM +0200, Luis R. Rodriguez wrote:
> Adding fsdevel for review on the correct semantics of handling signals on
> write(), in this case a sysfs write which triggered a sync request firmware
> call and what the firmware API should return in such case of a signal (I gather
> this should be -EINTR and not -ERESTARTSYS). Also whether or not SIGINT should
> be followed or if only allowing SIGKILL is fine (fine by me, but it would
> change old behaviour).
> 
> Hoping between fsdevel and linux-api folks we can hash this out.
> 
> On Tue, Jun 06, 2017 at 11:04:37AM +0200, Martin Fuzzey wrote:
> > On 05/06/17 22:24, Luis R. Rodriguez wrote:
> > > 
> > > 
> > > For these two reasons then it would seem best we do two things actually:
> > > 
> > > 1) return -EINTR instead of -EAGAIN when we detect swait_event_interruptible_timeout()
> > > got interrupted by a signal (it returns -ERESTARTSYS)
> > 
> > 
> > I disagree. That would force userspace to handle the signal rather than
> > having the kernel retry.
> > 
> > From Documentation/DocBook/kernel-hacking.tmpl:
> > 
> >    After you slept you should check if a signal occurred: the
> >    Unix/Linux way of handling signals is to temporarily exit the
> >    system call with the <constant>-ERESTARTSYS</constant> error.  The
> >    system call entry code will switch back to user context, process
> >    the signal handler and then your system call will be restarted
> >    (unless the user disabled that).  So you should be prepared to
> >    process the restart, e.g. if you're in the middle of manipulating
> >    some data structure.
> 
> This applies but you are missing my point that the LWN article [0] I referred
> to also stated "Kernel code which uses interruptible sleeps must always check
> to see whether it woke up as a result of a signal, and, if so, clean up
> whatever it was doing and return -EINTR back to user space." -- I realize there
> may be contradiction with above documentation -- this perhaps can be clarified
> with fsdevel folks *but* regardless of that the same article notes Alan Cox
> explains that "Unix tradition (and thus almost all applications) believe file
> store writes to be non signal interruptible. It would not be safe or practical
> to change that guarantee." So for this reason alone there does seem to be an
> exemption to the above documentation worth noting for file store writes, and
> the patch which you tested below *moves* the sysfs write op for firmware in
> that direction by adding a new killable swait.
> 
> [0] https://lwn.net/Articles/288056/                                                                                                                                          
>                                                                                                                                                                                 
> > > 2) Do as you note below and add wait_event_killable_timeout()
> > 
> > Hum,  I do think that would be better but, (please correct me if I'm wrong)
> > the _killable_ variants only allow SIGKILL  (and not SIGINT).
> 
> That seems correct given a TASK_KILLABLE is also TASK_UNINTERRUPTIBLE.
> 
> > 0cb64249ca "firmware_loader: abort request if wait_for_completion is
> > interrupted"
> > 
> > specifically mentrions ctrl-c (SIGINT) in the commit message so that would
> > no longer work.
> 
> Great point, but it *also* allowed SIGKILL, so I do feel the goal was also to
> allow it to be killable. I'm afraid that patch probably did not get proper
> review from sufficient folks and its worth now asking ourselves what we'd like
> to do.  I'm fine with letting go of SIGINT for firmware sysfs calls for the
> sake of keeping with the long standing unix tradition on write, given we *still
> have SIGKILL*.
> 
> > Myself I think having to use kill -9 to interrupt firmware loading by a
> > usespace helper is OK but others may disagree.
> 
> Its why I added fsdevel as well. This is really a semantics and uapi question.
> Between fsdevel and linux-api folks I would hope we can come to a sensible
> resolution.
> 
> > > I do not see why we could not introduce wait_event_killable_timeout()
> > > and swait_event_killable_timeout() into -stables.
> > > After seeing how simple it is to do so I tend to agree. Greg, Peter,
> > > what are your thoughts ?
> > > 
> > > Martin Fuzzey can you test this patch as an alternative to your issue ?
> > > 
> > > diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
> > > index b9f907eedbf7..70fc42e5e0da 100644
> > > --- a/drivers/base/firmware_class.c
> > > +++ b/drivers/base/firmware_class.c
> > > @@ -131,7 +131,7 @@ static int __fw_state_wait_common(struct fw_state *fw_st, long timeout)
> > >   {
> > >   	long ret;
> > > -	ret = swait_event_interruptible_timeout(fw_st->wq,
> > > +	ret = swait_event_killable_timeout(fw_st->wq,
> > >   				__fw_state_is_done(READ_ONCE(fw_st->status)),
> > >   				timeout);
> > >   	if (ret != 0 && fw_st->status == FW_STATUS_ABORTED)
> > > diff --git a/include/linux/swait.h b/include/linux/swait.h
> > > index c1f9c62a8a50..9c5ca2898b2f 100644
> > > --- a/include/linux/swait.h
> > > +++ b/include/linux/swait.h
> > > @@ -169,4 +169,29 @@ do {									\
> > >   	__ret;								\
> > >   })
> > > +#define __swait_event_killable(wq, condition)				\
> > > +	(void)___swait_event(wq, condition, TASK_KILLABLE, 0, schedule())
> > > +
> > > +#define swait_event_killable(wq, condition)				\
> > > +({									\
> > > +	int __ret = 0;							\
> > > +	if (!(condition))						\
> > > +		__ret = __swait_event_killable(wq, condition);		\
> > > +	__ret;								\
> > > +})
> > > +
> > > +#define __swait_event_killable_timeout(wq, condition, timeout)		\
> > > +	___swait_event(wq, ___wait_cond_timeout(condition),		\
> > > +		      TASK_INTERRUPTIBLE, timeout,			\
> > > +		      __ret = schedule_timeout(__ret))
> > > +
> > 
> > Should be TASK_KILLABLE above
> 
> Oops yes sorry.
> 
> > > +#define swait_event_killable_timeout(wq, condition, timeout)		\
> > > +({									\
> > > +	long __ret = timeout;						\
> > > +	if (!___wait_cond_timeout(condition))				\
> > > +		__ret = __swait_event_killable_timeout(wq,		\
> > > +						condition, timeout);	\
> > > +	__ret;								\
> > > +})
> > > +
> > >   #endif /* _LINUX_SWAIT_H */
> > > 
> > >    Luis
> > 
> > After replacing TASK_INTERRUPTIBLE with TASK_KILLABLE above it works for me.
> 
> Great, thanks for testing.
> 
>   Luis
> 

-- 
Luis Rodriguez, SUSE LINUX GmbH
Maxfeldstrasse 5; D-90409 Nuernberg

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#1658842 — Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback

> "Unix tradition (and thus almost all applications) believe file store
> writes to
> be non signal interruptible. It would not be safe or practical to
> change that
> guarantee."

Yep everyone codes

	write(disk_file, "foo", 3);

not while(..) blah around it.

> For these two reasons then it would seem best we do two things
> actually:
> 
> 1) return -EINTR instead of -EAGAIN when we detect
> swait_event_interruptible_timeout()
> got interrupted by a signal (it returns -ERESTARTSYS)
> 2) Do as you note below and add wait_event_killable_timeout()

Pedantic detail that I don't think affects you

If you have completed a part of the I/O then you should return the byte
processed count not EINTR, but -1,EINTR if no progress was made.

Alan

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#1658940 — Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback

Adding fsdevel folks.

On Tue, Jun 06, 2017 at 03:53:16PM +0100, Alan Cox wrote:
> > "Unix tradition (and thus almost all applications) believe file store
> > writes to
> > be non signal interruptible. It would not be safe or practical to
> > change that
> > guarantee."
> 
> Yep everyone codes
> 
> 	write(disk_file, "foo", 3);
> 
> not while(..) blah around it.

Thanks for the confirmation! That's a simple enough explanation.

> > For these two reasons then it would seem best we do two things
> > actually:
> > 
> > 1) return -EINTR instead of -EAGAIN when we detect
> > swait_event_interruptible_timeout()
> > got interrupted by a signal (it returns -ERESTARTSYS)
> > 2) Do as you note below and add wait_event_killable_timeout()
> 
> Pedantic detail that I don't think affects you
> 
> If you have completed a part of the I/O then you should return the byte
> processed count not EINTR, but -1,EINTR if no progress was made.

You are right with some new exceptions and with regards to the future:

The syfs loading interface for firmware currently goes through the
data file exposed on syfs, the respective write op firmware_data_write()
only checks for signals at the beginning. After that its a full one
swoop try to write if you are following the old tradition and are using
a buffer allocated by the firmware API.

If you are using the relatively new request_firmware_into_buf() added
by Stephen Boyd which lets the driver provide the allocated buffer then
we have a loop in firmware_rw() which should be fixed to:

1) Check for signals
2) Do what you noted above.

Furthermore Yi Li over at Intel is adding some new API calls which would
re-use some of this for FPGA firmwares which are also very large, that
work should consider the above and fix appropriately as well.

  Luis

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#1658994 — Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback

Using the right linux-fsdevel this time also, this was the second reply.

  Luis

On Tue, Jun 06, 2017 at 06:47:34PM +0200, Luis R. Rodriguez wrote:
> Adding fsdevel folks.
> 
> On Tue, Jun 06, 2017 at 03:53:16PM +0100, Alan Cox wrote:
> > > "Unix tradition (and thus almost all applications) believe file store
> > > writes to
> > > be non signal interruptible. It would not be safe or practical to
> > > change that
> > > guarantee."
> > 
> > Yep everyone codes
> > 
> > 	write(disk_file, "foo", 3);
> > 
> > not while(..) blah around it.
> 
> Thanks for the confirmation! That's a simple enough explanation.
> 
> > > For these two reasons then it would seem best we do two things
> > > actually:
> > > 
> > > 1) return -EINTR instead of -EAGAIN when we detect
> > > swait_event_interruptible_timeout()
> > > got interrupted by a signal (it returns -ERESTARTSYS)
> > > 2) Do as you note below and add wait_event_killable_timeout()
> > 
> > Pedantic detail that I don't think affects you
> > 
> > If you have completed a part of the I/O then you should return the byte
> > processed count not EINTR, but -1,EINTR if no progress was made.
> 
> You are right with some new exceptions and with regards to the future:
> 
> The syfs loading interface for firmware currently goes through the
> data file exposed on syfs, the respective write op firmware_data_write()
> only checks for signals at the beginning. After that its a full one
> swoop try to write if you are following the old tradition and are using
> a buffer allocated by the firmware API.
> 
> If you are using the relatively new request_firmware_into_buf() added
> by Stephen Boyd which lets the driver provide the allocated buffer then
> we have a loop in firmware_rw() which should be fixed to:
> 
> 1) Check for signals
> 2) Do what you noted above.
> 
> Furthermore Yi Li over at Intel is adding some new API calls which would
> re-use some of this for FPGA firmwares which are also very large, that
> work should consider the above and fix appropriately as well.
> 
>   Luis
> 

-- 
Luis Rodriguez, SUSE LINUX GmbH
Maxfeldstrasse 5; D-90409 Nuernberg

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#1659259 — Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback

On Tue, Jun 06, 2017 at 06:47:34PM +0200, Luis R. Rodriguez wrote:
> On Tue, Jun 06, 2017 at 03:53:16PM +0100, Alan Cox wrote:
> > Yep everyone codes
> > 
> > 	write(disk_file, "foo", 3);
> > 
> > not while(..) blah around it.

In general I/O to tty devices and other character mode devices was
where you definitely needed to check for EINTR/EAGAIN because that was
the place where historically Unix systems would interrupt system calls
--- e.g., a user typing control-Z, for example.

And in general writes to file systems and block devices in *general*
were never interrupted by signals, although that was always a
non-portable assumption.

So I've always subscribed to the "be liberal in what you accept,
conservative in what you send" rule of thumb.  Which is to say, any
programs *I* write I'll in general always check for EINTR/EAGAIN and
check for partial writes, but in general, as a kernel program I try to
adhere to the long-standing Unix trandition for disk based files.

This does beg the question about whether firmware devices are more
like tty devices or block devices or files, though.  If before signals
never caused them to return EINTR/EAGAIN, then it's probably best to
not break backwards compatbility.

That being said, not that you also have the option of using
-ERESTARTNOINTR (always restart the system call, regardless of how the
sighandle flags were set), and -ERESTARTNOHAND (restart the system
call always if there was no signal handler and the process was not
killed), in addition to -ERESTARTSYS.  So that might be another option
that's fairly easy to implement or experiment with.

       	      	      		   - Ted

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#1659312 — Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback

On Tue, Jun 06, 2017 at 06:11:51PM -0400, Theodore Ts'o wrote:
> On Tue, Jun 06, 2017 at 06:47:34PM +0200, Luis R. Rodriguez wrote:
> > On Tue, Jun 06, 2017 at 03:53:16PM +0100, Alan Cox wrote:
> > > Yep everyone codes
> > > 
> > > 	write(disk_file, "foo", 3);
> > > 
> > > not while(..) blah around it.
> 
> In general I/O to tty devices and other character mode devices was
> where you definitely needed to check for EINTR/EAGAIN because that was
> the place where historically Unix systems would interrupt system calls
> --- e.g., a user typing control-Z, for example.
> 
> And in general writes to file systems and block devices in *general*
> were never interrupted by signals, although that was always a
> non-portable assumption.
> 
> So I've always subscribed to the "be liberal in what you accept,
> conservative in what you send" rule of thumb.  Which is to say, any
> programs *I* write I'll in general always check for EINTR/EAGAIN and
> check for partial writes, but in general, as a kernel program I try to
> adhere to the long-standing Unix trandition for disk based files.

OK so userspace should consider checking for EINTR/EAGAIN.  On the kernel front
though we we do *strive* to go by the old unix tradition -- there are
exceptions though, of course.

> This does beg the question about whether firmware devices are more
> like tty devices or block devices or files, though.

And here you raise the analogy to see if its *worthy* to break the old unix
tradition, the tty example is a case that we seem to accept as reasonable
for an exception, clearly.

This help, thanks!

So, "firmware devices" is a misnomer, the firmware API does direct FS lookup
and only if that fails and the distribution enabled the fallback mechanism will
it be used if the file was not found on /lib/firmware/ paths. So the syfs
interface we are evaluating here is this fallback mechanism. The "firmware
device" then is really more a user of the firmware API, and these do vary
widely. In fact it recent developments with the "driver data API" generalize
the interface given things outside our typical device drivers for what we know
as old "firmware" are looking to use the firmware API for looking for files
from userspace. This in fact already has happened, it was just subtle: we look
for default EEPROMs, configururation files, microcode updates, and soon we'll
want to replace the userspace wireless CRDA tool for the regulatory database
with a simple file lookup once we get firmware signing upstream. So -- more and
more the API is being used for general file lookups.

Which type of drivers request these files ? It all varies across the board,
and we have really early things like CPU microcode files (so we enable built-in
files), regular old firmware files for things like networking drivers,
subsystem configuration stuff (for the wireless regulatory database), and it
seems now *huge* (100s of MiBs I'm told) for remote-proc and FPGAs. The FPGA
use case is one use case where having the uploader use a while loop makes more
sense. Drivers may also want to have more fine control to the buffer where the
"driver data" gets stashed into, so the API request_firmware_into_buf() was
added for this purpose. The FPGA devices seem to want to use this breakdown
mechanism as well. Although the remote-proc folks seem to be relying on the
sysfs interface as a default mechanism.

So it would seem to make sense to support the loop thing since some
files these days *can* be really big. I think we can easily address
this by relying on the killable signal (SIGKILL), rather than capturing
SIGINT (CTRL-C).

One problem is we had supported SIGINT before, it was reported however we
never gave back to userspace the fact that a signal was captured, we always
returned EAGAIN, so usersace did not know WTF was going on. The reporter wanted
to detect this and wanted to get us to return the same value the wait call
passed to the firmware API, -ERESTARTSYS. Hence this patch, however since
-ERESTARTSYS is special and folks may just restart the syscall always when this
happens, one question is if we should return EINTR instead of today's EAGAIN.

> If before signals
> never caused them to return EINTR/EAGAIN, then it's probably best to
> not break backwards compatbility.

There was a time where did not have signal, and always just used to return
-ENOMEM on failure. After signals support was added we still were
returning -ENOMEM for a while. It was only later that we started capturing
the actual signal, however this was masked as EAGAIN, for no precise good
reason, I suppose just lack of review.

The patch in question wants us to return -ERESTARTSYS so that userspace
can restart the upload. But the issue was that the sysfs firmware loader
was killed by a signal as well, so this is why Dmitry noted that we can
just fix this issue by just making the wait killable with SIGKILL only.
The swait killable patch I supplied upon Dmitry's suggestion as a replacement
would do away with capturing SIGINT but allow SIGKILL then.

Since EAGAIN was always returned even if a signal was captured I'm
inclined to take the position we really never gave userspace a proper
clue about the signal. Additionally I cannot see why userspace would
rely on SIGINT working *only* but not *SIGKILL*.

The risk here I think is if userspace ever *did* rely on SIGINT for the sysfs
interface as userspace functional API. If this is not worth breaking
then I suppose we are stuck with the current wait. If we do that I'd
say we return EINTR, based on what I have read so far.

If doing away with SIGINT but keeping SIGKILL is rather sane then I'd go
with the approach of the new swait killable + returning -EINTR.

> That being said, note that you also have the option of using
> -ERESTARTNOINTR (always restart the system call, regardless of how the
> sighandle flags were set), and -ERESTARTNOHAND (restart the system
> call always if there was no signal handler and the process was not
> killed), in addition to -ERESTARTSYS.

We rely on swait, and swait right now only uses -ERESTARTSYS. Are
you saying we could mask out -ERESTARTSYS and map it to -ERESTARTNOINTR
or -ERESTARTNOHAND if we see fit for some future functionality / need ?

> So that might be another option
> that's fairly easy to implement or experiment with.

Thanks!

  Luis

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#1659373

On Tue, Jun 6, 2017 at 5:22 PM, Luis R. Rodriguez <mcgrof@kernel.org> wrote:
> On Tue, Jun 06, 2017 at 06:11:51PM -0400, Theodore Ts'o wrote:
>> On Tue, Jun 06, 2017 at 06:47:34PM +0200, Luis R. Rodriguez wrote:
>> > On Tue, Jun 06, 2017 at 03:53:16PM +0100, Alan Cox wrote:
>
> We rely on swait, and swait right now only uses -ERESTARTSYS. Are
> you saying we could mask out -ERESTARTSYS and map it to -ERESTARTNOINTR
> or -ERESTARTNOHAND if we see fit for some future functionality / need ?

I think that has essentially nothing to do with swait.  User code does
some syscall.  That syscall triggers a firmware load.  The caller gets
a signal.  If you're going to let firmware load get interrupted, you
need to consider what the syscall is.

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#1659401 — Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback

On Tue, Jun 06, 2017 at 09:56:47PM -0700, Andy Lutomirski wrote:
> On Tue, Jun 6, 2017 at 5:22 PM, Luis R. Rodriguez <mcgrof@kernel.org> wrote:
> > On Tue, Jun 06, 2017 at 06:11:51PM -0400, Theodore Ts'o wrote:
> >> On Tue, Jun 06, 2017 at 06:47:34PM +0200, Luis R. Rodriguez wrote:
> >> > On Tue, Jun 06, 2017 at 03:53:16PM +0100, Alan Cox wrote:
> >
> > We rely on swait, and swait right now only uses -ERESTARTSYS. Are
> > you saying we could mask out -ERESTARTSYS and map it to -ERESTARTNOINTR
> > or -ERESTARTNOHAND if we see fit for some future functionality / need ?
> 
> I think that has essentially nothing to do with swait.  User code does
> some syscall.  That syscall triggers a firmware load.  The caller gets
> a signal.  If you're going to let firmware load get interrupted, you
> need to consider what the syscall is.

I think it is way too complicated and I do not think driver writers will
stand a chance of implementing this correctly, given that often firmware
load might be triggered indirectly and by multitude of syscalls.

What's wrong with saying that the only way to interrupt firmware loading
is to kill the process? So ctrl-c will no longer interrupt it, but I do
not think that ease of aborting firmware update is primary goal here. I
consider simple is good here.

Thanks.

-- 
Dmitry

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#1659741 — Re: [PATCH v2] firmware: fix sending -ERESTARTSYS due to signal on fallback

> What's wrong with saying that the only way to interrupt firmware
> loading is to kill the process? So ctrl-c will no longer interrupt
> it, but I do not think that ease of aborting firmware update is
> primary goal here. I consider simple is good here.

Agreed 100%. The user process did not ask for firmware load, it asked
for an I/O operation. Semantically it should appear as if someone else
did the firmware load and it just had to wait for it to happen.

Alan

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#1651687

On Fri, May 26, 2017 at 2:26 PM, Dmitry Torokhov
<dmitry.torokhov@gmail.com> wrote:
> On Fri, May 26, 2017 at 12:46 PM, Luis R. Rodriguez <mcgrof@kernel.org> wrote:
>> On Fri, May 26, 2017 at 06:09:29AM -0500, Eric W. Biederman wrote:
>>> "Fuzzey, Martin" <mfuzzey@parkeon.com> writes:
>>> >>>> Maybe SIGCHLD shouldn't interrupt firmware loading?
>>> >
>>> > I don't think there's a way of doing that without disabling all
>>> > signals (ie using the non interruptible wait variants).
>>> > It used to be that way (which is why I only ran into this after
>>> > updating from an ancient 3.16 kernel to a slightly less ancient 4.4)
>>> > But there are valid reasons for wanting to be able to interrupt
>>> > firmware loading (like being able to kill the userspace helper)
>>>
>>> Perhaps simply using a killable wait and not a fully interruptible
>>> wait would be better?
>>
>> What do you mean by a killable wait BTW?
>
> https://lwn.net/Articles/288056/
>
> I think only interrupting firmware loading with fatal signals would
> make a lot of sense.
>
>>
>> ret = swait_event_interruptible_timeout() is being used right now.
>
> It looks like we are missing swait_event_killable*(), but I do not
> think it would be hard to add.

What should we do for stable ? Is this a *stable* issue ?

 Luis

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