Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
Groups > linux.kernel > #1732524
| From | Jaegeuk Kim <jaegeuk@kernel.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion |
| Date | 2017-09-14 21:20 +0200 |
| Message-ID | <upHQ5-Dd-5@gated-at.bofh.it> (permalink) |
| References | (2 earlier) <uppqa-5wg-7@gated-at.bofh.it> <uppzP-5zs-1@gated-at.bofh.it> <upqYV-6zf-1@gated-at.bofh.it> <uprih-6FS-3@gated-at.bofh.it> <upHdo-aN-23@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On 09/14, Al Viro wrote:
> On Thu, Sep 14, 2017 at 02:30:17AM +0100, Al Viro wrote:
> > On Wed, Sep 13, 2017 at 06:10:48PM -0700, Jaegeuk Kim wrote:
> >
> > > Android triggers umount(2) by init process, which is definitely not a kernel
> > > thread. But, we've seen some kernel panics which say umount(2) was succeeded,
> > > but ext4 triggered a kernel panic due to EIO after then like below. I'm also
> > > not sure task_work_run() would be also safe enoughly. May I ask where I can
> > > find sys_umount() calls task_work_run()?
> >
> > ret_{fast,slow}_syscall ->
> > slow_work_pending ->
> > do_work_pending() ->
> > tracehook_notify_resume() ->
> > task_work_run()
> >
> > It's not sys_umount() (or any other sys_...()) - it's syscall dispatcher after
> > having called one of those and before returning to userland. What is guaranteed
> > is that after successful task_work_add() the damn thing will be run in context
> > of originating process before it returns from syscall. So any subsequent
> > syscalls from that process are guaranteed to happen after the work has run.
> > The same happens if the process exits rather than returns to userland (do_exit() ->
> > exit_task_work() -> task_work_run()), but for that you would need it to die in
> > umount(2) (e.g. get kill -9 delivered on the way out).
> >
> > Please, check if you are seeing task_work_add() failure in there and if you do,
> > I would like to see a stack trace. IOW, slap WARN_ON(1); right after
> > if (!task_work_add(task, &mnt->mnt_rcu, true))
> > return;
> > and see what (if anything) gets printed.
>
> AFAICS, for task_work_add() to fail here we need a final mntput() to be run
> in context of a thread that already had exit_signals() run *and* subsequent
> task_work_run() run to completion (with all pending callbacks executed, along
> with all callbacks added by those, etc.)
>
> For that to have happened during umount(2) we would've needed
> * killing signal delivered while going through the syscall
> * final mntput() to have been done *NOT* from sys_umount() (otherwise
> the work would've been added before we got to exit_signals())
> * final mntput() to have been done *NOT* from any task_work callbacks
> (otherwise it would've been added before we'd observed a combination of empty
> list of pending work with PF_EXITING)
>
> I really want to see the stack trace of that failing task_work_add(), if that's
> what actually happens there. What kind of a reproducer do you have for that?
I've got this error from Android user, so there's no reproducer unfortunately.
So, I wrote a script capturing WARN_ON after reboot running at every minute, but
couldn't have got the error since yesterday so far.
Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
[PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-13 22:20 +0200
Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-14 01:10 +0200
Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-14 01:40 +0200
Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-14 01:50 +0200
Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-14 03:20 +0200
Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-14 03:40 +0200
Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-14 20:40 +0200
Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-14 21:20 +0200
Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-15 02:20 +0200
Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-15 04:10 +0200
Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-15 05:50 +0200
Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-15 06:30 +0200
Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-15 20:50 +0200
Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion Theodore Ts'o <tytso@mit.edu> - 2017-09-16 00:20 +0200
Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-16 01:30 +0200
Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-16 01:50 +0200
Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-19 18:00 +0200
Re: [PATCH] vfs: introduce UMOUNT_WAIT which waits for umount completion Amir Goldstein <amir73il@gmail.com> - 2017-09-16 09:20 +0200
Re: [PATCH v2] vfs: introduce UMOUNT_WAIT which waits for umount completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-20 19:40 +0200
Re: [PATCH v2] vfs: introduce UMOUNT_WAIT which waits for umount completion Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-20 20:40 +0200
Re: [PATCH v2] vfs: introduce UMOUNT_WAIT which waits for umount completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-21 02:40 +0200
Re: [PATCH v2] vfs: introduce UMOUNT_WAIT which waits for umount completion Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-21 04:50 +0200
Re: [PATCH v2] vfs: introduce UMOUNT_WAIT which waits for umount completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-21 07:10 +0200
Re: [PATCH v2] vfs: introduce UMOUNT_WAIT which waits for umount completion Theodore Ts'o <tytso@mit.edu> - 2017-09-21 17:00 +0200
Re: [PATCH v2] vfs: introduce UMOUNT_WAIT which waits for umount completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-21 19:20 +0200
Re: [PATCH v3] vfs: introduce UMOUNT_WAIT to wait for delayed_fput/mntput completion Jaegeuk Kim <jaegeuk@kernel.org> - 2017-09-21 20:30 +0200
csiph-web