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Bug#820567: kexec on mipsel partially broken between ckt20 and ckt25

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  Bug#820567: kexec on mipsel partially broken between ckt20 and ckt25 Elliott Mitchell <ehem+debian@m5p.com> - 2016-04-10 03:40 +0200
    Bug#820567: kexec on mipsel partially broken between ckt20 and ckt25 Ben Hutchings <ben@decadent.org.uk> - 2016-04-10 11:20 +0200
      Bug#820567: kexec on mipsel partially broken between ckt20 and ckt25 Elliott Mitchell <ehem+debian@m5p.com> - 2016-04-10 20:20 +0200
        Bug#820567: kexec on mipsel partially broken between ckt20 and ckt25 Ben Hutchings <ben@decadent.org.uk> - 2016-04-10 21:00 +0200
          Bug#820567: kexec on mipsel partially broken between ckt20 and ckt25 Elliott Mitchell <ehem+debian@m5p.com> - 2016-04-10 23:40 +0200
            Bug#820567: kexec on mipsel partially broken between ckt20 and ckt25 Ben Hutchings <ben@decadent.org.uk> - 2016-04-11 02:40 +0200
              Bug#820567: kexec on mipsel partially broken between ckt20 and ckt25 Elliott Mitchell <ehem+debian@m5p.com> - 2016-04-11 08:00 +0200
    Processed: Re: Bug#820567: kexec on mipsel partially broken  between ckt20 and ckt25 owner@bugs.debian.org (Debian Bug Tracking System) - 2016-04-10 11:20 +0200
    Processed: Re: Bug#820567: kexec on mipsel partially broken  between ckt20 and ckt25 owner@bugs.debian.org (Debian Bug Tracking System) - 2016-04-10 21:00 +0200
    Bug#820567: marked as done (kexec on mipsel partially broken  between ckt20 and ckt25) owner@bugs.debian.org (Debian Bug Tracking System) - 2016-04-11 13:40 +0200

#53510 — Bug#820567: kexec on mipsel partially broken between ckt20 and ckt25

Package: linux-source-3.16
Version: 3.16.7-ckt25-1~bpo70+1

Between 3.16.7-ctk20 and 3.16.7-ctk25 the kexec functionality of the
Linux kernel was damaged.  The system I'm looking at uses a 3.3 kernel
to load the "real" kernel off a filesystem and kexec into that.  The 3.3
kernel was able to successfully kexec into a 3.16.7-ctk20 kernel, but
is unable to kexec into a 3.16.7-ctk25 kernel.  However I found the
3.16.7-ctk20 IS able to successfully kexec the 3.16.7-ctk25 kernel.

Doing a double-kexec does work around the issue, but it means I need to
hold onto that one magic kernel for the moment...

In other news, it appears sometime between 3.3 and 3.10 there started
being a requirement for GCC 4.8 on mipsel.


-- 
(\___(\___(\______          --=> 8-) EHM <=--          ______/)___/)___/)
 \BS (    |         EHeM+sigmsg@m5p.com  PGP 87145445         |    )   /
  \_CS\   |  _____  -O #include <stddisclaimer.h> O-   _____  |   /  _/
8A19\___\_|_/58D2 7E3D DDF4 7BA6 <-PGP-> 41D1 B375 37D0 8714\_|_/___/5445

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#53514

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Control: reassign -1 src:linux 3.16.7-ckt25-1

On Sat, 2016-04-09 at 18:31 -0700, Elliott Mitchell wrote:
> Package: linux-source-3.16
> Version: 3.16.7-ckt25-1~bpo70+1
> 
> Between 3.16.7-ctk20 and 3.16.7-ctk25 the kexec functionality of the
> Linux kernel was damaged.  The system I'm looking at uses a 3.3 kernel
> to load the "real" kernel off a filesystem and kexec into that.  The 3.3
> kernel was able to successfully kexec into a 3.16.7-ctk20 kernel, but
> is unable to kexec into a 3.16.7-ctk25 kernel.  However I found the
> 3.16.7-ctk20 IS able to successfully kexec the 3.16.7-ctk25 kernel.

Surely this is a bug in the built-in (3.3) kernel, not the new one?  If
there's something simple that can be done in the Debian kernel to work
around this, we should do that, but otherwise you're stuck with this.

> Doing a double-kexec does work around the issue, but it means I need to
> hold onto that one magic kernel for the moment...
> 
> In other news, it appears sometime between 3.3 and 3.10 there started
> being a requirement for GCC 4.8 on mipsel.

Packages in jessie must be buildable using compiler versions in jessie.
That means either gcc-4.8 or gcc-4.9.

Ben.

-- 
Ben Hutchings
I'm always amazed by the number of people who take up solipsism because
they heard someone else explain it. - E*Borg on alt.fan.pratchett

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#53521

On Sun, Apr 10, 2016 at 10:09:38AM +0100, Ben Hutchings wrote:
> On Sat, 2016-04-09 at 18:31 -0700, Elliott Mitchell wrote:
> > Between 3.16.7-ctk20 and 3.16.7-ctk25 the kexec functionality of the
> > Linux kernel was damaged.????The system I'm looking at uses a 3.3 kernel
> > to load the "real" kernel off a filesystem and kexec into that.????The 3.3
> > kernel was able to successfully kexec into a 3.16.7-ctk20 kernel, but
> > is unable to kexec into a 3.16.7-ctk25 kernel.????However I found the
> > 3.16.7-ctk20 IS able to successfully kexec the 3.16.7-ctk25 kernel.
> 
> Surely this is a bug in the built-in (3.3) kernel, not the new one? ??If
> there's something simple that can be done in the Debian kernel to work
> around this, we should do that, but otherwise you're stuck with this.

This is certainly a reasonable theory.  Alas, I cannot speak to which of
these theories is correct.  All I can say for certain is that something
changed between ctk20 and ctk25 which made the 3.3 kernel unable to kexec
ctk25.  I'm under the impression as of 3.3 the kexec functionality was
supposed to be stable on MIPS, but that could be incorrect.

I should also note, during the failed kexecs I would see the messages
from the 3.3 kernel saying the kexec was starting, but never see any
messages from the ctk25 kernel.  Unless someone wants to send me a JTAG
decoder that is all I can say.


> > Doing a double-kexec does work around the issue, but it means I need to
> > hold onto that one magic kernel for the moment...
> > 
> > In other news, it appears sometime between 3.3 and 3.10 there started
> > being a requirement for GCC 4.8 on mipsel.
> 
> Packages in jessie must be buildable using compiler versions in jessie.
> That means either gcc-4.8 or gcc-4.9.

linux-source-3.16 is available as a backport to wheezy, which does not
feature gcc-4.8.


-- 
(\___(\___(\______          --=> 8-) EHM <=--          ______/)___/)___/)
 \BS (    |         EHeM+sigmsg@m5p.com  PGP 87145445         |    )   /
  \_CS\   |  _____  -O #include <stddisclaimer.h> O-   _____  |   /  _/
8A19\___\_|_/58D2 7E3D DDF4 7BA6 <-PGP-> 41D1 B375 37D0 8714\_|_/___/5445

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#53524

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Control: tag -1 moreinfo

On Sun, 2016-04-10 at 11:09 -0700, Elliott Mitchell wrote:
> On Sun, Apr 10, 2016 at 10:09:38AM +0100, Ben Hutchings wrote:
> > 
> > On Sat, 2016-04-09 at 18:31 -0700, Elliott Mitchell wrote:
> > > 
> > > Between 3.16.7-ctk20 and 3.16.7-ctk25 the kexec functionality of the
> > > Linux kernel was damaged.????The system I'm looking at uses a 3.3 kernel
> > > to load the "real" kernel off a filesystem and kexec into that.????The 3.3
> > > kernel was able to successfully kexec into a 3.16.7-ctk20 kernel, but
> > > is unable to kexec into a 3.16.7-ctk25 kernel.????However I found the
> > > 3.16.7-ctk20 IS able to successfully kexec the 3.16.7-ctk25 kernel.
> > Surely this is a bug in the built-in (3.3) kernel, not the new one? ??If
> > there's something simple that can be done in the Debian kernel to work
> > around this, we should do that, but otherwise you're stuck with this.
> This is certainly a reasonable theory.  Alas, I cannot speak to which of
> these theories is correct.  All I can say for certain is that something
> changed between ctk20 and ctk25 which made the 3.3 kernel unable to kexec
> ctk25.  I'm under the impression as of 3.3 the kexec functionality was
> supposed to be stable on MIPS, but that could be incorrect.
> 
> I should also note, during the failed kexecs I would see the messages
> from the 3.3 kernel saying the kexec was starting, but never see any
> messages from the ctk25 kernel.  Unless someone wants to send me a JTAG
> decoder that is all I can say.

One of the MIPS porters may be able to help you, but I have no idea
what to suggest.

Are you using one of the linux-image packages or building from source
with your own configuration?  In the latter case, are you sure you used
the same configuration for old and new kernels?

> > > Doing a double-kexec does work around the issue, but it means I need to
> > > hold onto that one magic kernel for the moment...
> > > 
> > > In other news, it appears sometime between 3.3 and 3.10 there started
> > > being a requirement for GCC 4.8 on mipsel.
> > Packages in jessie must be buildable using compiler versions in jessie.
> > That means either gcc-4.8 or gcc-4.9.
> linux-source-3.16 is available as a backport to wheezy, which does not
> feature gcc-4.8.

That in no way contradicts what I said. :-)  When I backport the linux
source package from jessie to wheezy I change it to use gcc-4.6.

But the linux-source-X.Y packages (which are a different thing to the
linux source package!) don't specify any particular compiler version.
You can choose that with the CC variable; otherwise the default
compiler (specified by the gcc package) will be used.

Ben.

-- 
Ben Hutchings
I'm always amazed by the number of people who take up solipsism because
they heard someone else explain it. - E*Borg on alt.fan.pratchett

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#53535

On Sun, Apr 10, 2016 at 07:47:28PM +0100, Ben Hutchings wrote:
> On Sun, 2016-04-10 at 11:09 -0700, Elliott Mitchell wrote:
> > On Sun, Apr 10, 2016 at 10:09:38AM +0100, Ben Hutchings wrote:
> > > 
> > > On Sat, 2016-04-09 at 18:31 -0700, Elliott Mitchell wrote:
> > > > 
> > > > Between 3.16.7-ctk20 and 3.16.7-ctk25 the kexec functionality of the
> > > > Linux kernel was damaged.????The system I'm looking at uses a 3.3 kernel
> > > > to load the "real" kernel off a filesystem and kexec into that.????The 3.3
> > > > kernel was able to successfully kexec into a 3.16.7-ctk20 kernel, but
> > > > is unable to kexec into a 3.16.7-ctk25 kernel.????However I found the
> > > > 3.16.7-ctk20 IS able to successfully kexec the 3.16.7-ctk25 kernel.
> > > Surely this is a bug in the built-in (3.3) kernel, not the new one? ??If
> > > there's something simple that can be done in the Debian kernel to work
> > > around this, we should do that, but otherwise you're stuck with this.
> > This is certainly a reasonable theory.????Alas, I cannot speak to which of
> > these theories is correct.????All I can say for certain is that something
> > changed between ctk20 and ctk25 which made the 3.3 kernel unable to kexec
> > ctk25.????I'm under the impression as of 3.3 the kexec functionality was
> > supposed to be stable on MIPS, but that could be incorrect.
> > 
> > I should also note, during the failed kexecs I would see the messages
> > from the 3.3 kernel saying the kexec was starting, but never see any
> > messages from the ctk25 kernel.????Unless someone wants to send me a JTAG
> > decoder that is all I can say.
> 
> One of the MIPS porters may be able to help you, but I have no idea
> what to suggest.
> 
> Are you using one of the linux-image packages or building from source
> with your own configuration? ??In the latter case, are you sure you used
> the same configuration for old and new kernels?

Building from source.  The .config files used started identical, but
looks like things changed in the Kconfig files which caused 4 items to
switch from 'm' to 'y' (all networking, which shouldn't cause the
observed bug).  There were also some patches derived from OpenWRT's
patches, but those did not change at all.


> > > > Doing a double-kexec does work around the issue, but it means I need to
> > > > hold onto that one magic kernel for the moment...
> > > > 
> > > > In other news, it appears sometime between 3.3 and 3.10 there started
> > > > being a requirement for GCC 4.8 on mipsel.
> > > Packages in jessie must be buildable using compiler versions in jessie.
> > > That means either gcc-4.8 or gcc-4.9.
> > linux-source-3.16 is available as a backport to wheezy, which does not
> > feature gcc-4.8.
> 
> That in no way contradicts what I said. :-) ??When I backport the linux
> source package from jessie to wheezy I change it to use gcc-4.6.
> 
> But the linux-source-X.Y packages (which are a different thing to the
> linux source package!) don't specify any particular compiler version.
> You can choose that with the CC variable; otherwise the default
> compiler (specified by the gcc package) will be used.

For this particular mipsel device I was unable to kexec the kernel unless
it was built with GCC-4.8.  If the kernel was built with GCC-4.7 or
earlier, I got symptoms identical to the above, messages from the old
kernel on the console serial port that it was going away and kexec'd
kernel never output any messages.  I could believe this is a funky
compiler issue.


-- 
(\___(\___(\______          --=> 8-) EHM <=--          ______/)___/)___/)
 \BS (    |         EHeM+sigmsg@m5p.com  PGP 87145445         |    )   /
  \_CS\   |  _____  -O #include <stddisclaimer.h> O-   _____  |   /  _/
8A19\___\_|_/58D2 7E3D DDF4 7BA6 <-PGP-> 41D1 B375 37D0 8714\_|_/___/5445

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#53539

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On Sun, 2016-04-10 at 14:32 -0700, Elliott Mitchell wrote:
> On Sun, Apr 10, 2016 at 07:47:28PM +0100, Ben Hutchings wrote:
> > 
> > On Sun, 2016-04-10 at 11:09 -0700, Elliott Mitchell wrote:
> > > 
> > > On Sun, Apr 10, 2016 at 10:09:38AM +0100, Ben Hutchings wrote:
> > > > 
> > > > 
> > > > On Sat, 2016-04-09 at 18:31 -0700, Elliott Mitchell wrote:
[...]
> > > > > Doing a double-kexec does work around the issue, but it means I need to
> > > > > hold onto that one magic kernel for the moment...
> > > > > 
> > > > > In other news, it appears sometime between 3.3 and 3.10 there started
> > > > > being a requirement for GCC 4.8 on mipsel.
> > > > Packages in jessie must be buildable using compiler versions in jessie.
> > > > That means either gcc-4.8 or gcc-4.9.
> > > linux-source-3.16 is available as a backport to wheezy, which does not
> > > feature gcc-4.8.
> > That in no way contradicts what I said. :-) ??When I backport the linux
> > source package from jessie to wheezy I change it to use gcc-4.6.
> > 
> > But the linux-source-X.Y packages (which are a different thing to the
> > linux source package!) don't specify any particular compiler version.
> > You can choose that with the CC variable; otherwise the default
> > compiler (specified by the gcc package) will be used.
> For this particular mipsel device I was unable to kexec the kernel unless
> it was built with GCC-4.8.

I see.

> If the kernel was built with GCC-4.7 or
> earlier, I got symptoms identical to the above, messages from the old
> kernel on the console serial port that it was going away and kexec'd
> kernel never output any messages.  I could believe this is a funky
> compiler issue.

Could it be the kernel image is close to a critical size limit?  The
kernel typically gets slightly larger with each stable update.  Does
gcc 4.8 generate a smaller or larger kernel image than older versions?

Ben.

-- 
Ben Hutchings
Humans are not rational beings; they are rationalising beings.

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#53542

On Mon, Apr 11, 2016 at 01:34:56AM +0100, Ben Hutchings wrote:
> On Sun, 2016-04-10 at 14:32 -0700, Elliott Mitchell wrote:
> > On Sun, Apr 10, 2016 at 07:47:28PM +0100, Ben Hutchings wrote:
> > > That in no way contradicts what I said. :-) ??When I backport the linux
> > > source package from jessie to wheezy I change it to use gcc-4.6.
> > > 
> > > But the linux-source-X.Y packages (which are a different thing to the
> > > linux source package!) don't specify any particular compiler version.
> > > You can choose that with the CC variable; otherwise the default
> > > compiler (specified by the gcc package) will be used.
> > For this particular mipsel device I was unable to kexec the kernel unless
> > it was built with GCC-4.8.
> 
> I see.
> 
> > If the kernel was built with GCC-4.7 or
> > earlier, I got symptoms identical to the above, messages from the old
> > kernel on the console serial port that it was going away and kexec'd
> > kernel never output any messages.????I could believe this is a funky
> > compiler issue.
> 
> Could it be the kernel image is close to a critical size limit? ??The
> kernel typically gets slightly larger with each stable update. ??Does
> gcc 4.8 generate a smaller or larger kernel image than older versions?

You win one and lose one.  I tracked down the configuration option that
managed to switch from "y" to "n" (seems my base config had it as "y",
but other options interfered, now it is "m"), that shrank the kernel by
40KB and the resultant kernel was successfully loaded by the 3.3 kernel.

The kernel built with GCC 4.4 was about 2% larger than the GCC 4.8 build,
while a GCC 4.6 build was less than 1% smaller than the GCC 4.8 build.
Neither of these kernels was able to successfully start when kexec'd by
a 3.16 kernel (which *was* able to start the bigger kernel).


So this solves the problem this bug was about, it was a size issue.  :-(

Alas I'm expecting it to be a while before I can get the proper solution
in place.


-- 
(\___(\___(\______          --=> 8-) EHM <=--          ______/)___/)___/)
 \BS (    |         EHeM+sigmsg@m5p.com  PGP 87145445         |    )   /
  \_CS\   |  _____  -O #include <stddisclaimer.h> O-   _____  |   /  _/
8A19\___\_|_/58D2 7E3D DDF4 7BA6 <-PGP-> 41D1 B375 37D0 8714\_|_/___/5445

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#53517 — Processed: Re: Bug#820567: kexec on mipsel partially broken between ckt20 and ckt25

Processing control commands:

> reassign -1 src:linux 3.16.7-ckt25-1
Bug #820567 [linux-source-3.16] kexec on mipsel partially broken between ckt20 and ckt25
Bug reassigned from package 'linux-source-3.16' to 'src:linux'.
No longer marked as found in versions linux/3.16.7-ckt25-1~bpo70+1.
Ignoring request to alter fixed versions of bug #820567 to the same values previously set
Bug #820567 [src:linux] kexec on mipsel partially broken between ckt20 and ckt25
Marked as found in versions linux/3.16.7-ckt25-1.

-- 
820567: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=820567
Debian Bug Tracking System
Contact owner@bugs.debian.org with problems

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#53525 — Processed: Re: Bug#820567: kexec on mipsel partially broken between ckt20 and ckt25

Processing control commands:

> tag -1 moreinfo
Bug #820567 [src:linux] kexec on mipsel partially broken between ckt20 and ckt25
Added tag(s) moreinfo.

-- 
820567: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=820567
Debian Bug Tracking System
Contact owner@bugs.debian.org with problems

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#53546 — Bug#820567: marked as done (kexec on mipsel partially broken between ckt20 and ckt25)

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Your message dated Mon, 11 Apr 2016 12:26:40 +0100
with message-id <1460374000.25201.18.camel@decadent.org.uk>
and subject line Re: Bug#820567: kexec on mipsel partially broken between ckt20 and ckt25
has caused the Debian Bug report #820567,
regarding kexec on mipsel partially broken between ckt20 and ckt25
to be marked as done.

This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.

(NB: If you are a system administrator and have no idea what this
message is talking about, this may indicate a serious mail system
misconfiguration somewhere. Please contact owner@bugs.debian.org
immediately.)


-- 
820567: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=820567
Debian Bug Tracking System
Contact owner@bugs.debian.org with problems

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