From: Ming Lei <ming.lei@redhat.com>
To: Luis Chamberlain <mcgrof@kernel.org>
Cc: Miroslav Benes <mbenes@suse.cz>,
tj@kernel.org, gregkh@linuxfoundation.org,
akpm@linux-foundation.org, minchan@kernel.org, jeyu@kernel.org,
shuah@kernel.org, bvanassche@acm.org, dan.j.williams@intel.com,
joe@perches.com, tglx@linutronix.de, keescook@chromium.org,
rostedt@goodmis.org, linux-spdx@vger.kernel.org,
linux-doc@vger.kernel.org, linux-block@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org,
linux-kernel@vger.kernel.org, ming.lei@redhat.com
Subject: Re: [PATCH v8 09/12] sysfs: fix deadlock race with module removal
Date: Wed, 13 Oct 2021 23:04:07 +0800 [thread overview]
Message-ID: <YWb1Z7EXruo6gaEp@T590> (raw)
In-Reply-To: <YWbSk6p3bfXUPZ92@bombadil.infradead.org>
On Wed, Oct 13, 2021 at 05:35:31AM -0700, Luis Chamberlain wrote:
> On Wed, Oct 13, 2021 at 09:07:03AM +0800, Ming Lei wrote:
> > On Tue, Oct 12, 2021 at 02:18:28PM -0700, Luis Chamberlain wrote:
> > > > Looks test_sysfs isn't in linus tree, where can I find it?
> > >
> > > https://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux-next.git/log/?h=20210927-sysfs-generic-deadlock-fix
> > >
> > > To reproduce the deadlock revert the patch in this thread and then run
> > > either of these two tests as root:
> > >
> > > ./tools/testing/selftests/sysfs/sysfs.sh -w 0027
> > > ./tools/testing/selftests/sysfs/sysfs.sh -w 0028
> > >
> > > You will need to enable the test_sysfs driver.
> > > > Can you share the code which waits for the sysfs / kernfs files to be
> > > > stop being used?
> > >
> > > How about a call trace of the two tasks which deadlock, here is one of
> > > running test 0027:
> > >
> > > kdevops login: [ 363.875459] INFO: task sysfs.sh:1271 blocked for more
> > > than 120 seconds.
>
> <-- snip -->
>
> > That doesn't show the deadlock is related with module_exit().
>
> Not directly no.
Then the patch title of 'sysfs: fix deadlock race with module removal'
is wrong.
>
> > It is clearly one AA deadlock, what I meant was that it isn't related with
> > module exit cause lock & device_del() isn't always done in module exit, so
> > I doubt your fix with grabbing module refcnt is good or generic enough.
>
> A device_del() *can* happen in other areas other than module exit sure,
> but the issue is if a shared lock is used *before* device_del() and also
> used on a sysfs op. Typically this can happen on module exit, and the
> other common use case in my experience is on sysfs ops, such is the case
> with the zram driver. Both cases are covered then by this fix.
Again, can you share the related zram code about the issue? In
zram_drv.c of linus or next tree, I don't see any lock is held before
calling del_gendisk().
>
> If there are other areas, that is still driver specific, but of the
> things we *can* generalize, definitely module exit is a common path.
>
> > Except for your cooked test_sys module, how many real drivers do suffer the
> > problem? What are they?
>
> I only really seriously considered trying to generalize this after it
IMO your generalization isn't good or correct because this kind of issue
is _not_ related with module exit at all. What matters is just that one lock is
held before calling device_del(), meantime the same lock is required
in the device's attribute show/store function().
There are many cases in which we call device_del() not from module_exit(),
such as scsi scan, scsi sysfs store(), or even handling event from
device side, nvme error handling, usb hotplug, ...
> was hinted to me live patching was also affected, and so clearly
> something generic was desirable.
It might be just the only two drivers(zram and live patch) with this bug, and
it is one simply AA bug in driver. Not mention I don't see such usage in
zram_drv.c.
>
> There may be other drivers for sure, but a hunt for that with semantics
> would require a bit complex coccinelle patch with iteration support.
>
> > Why can't we fix the exact driver?
>
> You can try, the way the lock is used in zram is correct, specially
What is the lock in zram? Again can you share the related functions?
> after my other fix in this series which addresses another unrelated bug
> with cpu hotplug multistate support. So we then can proceed to either
> take the position to say: "Thou shalt not use a shared lock on module
> exit and a sysfs op" and try to fix all places, or we generalize a fix
> for this. A generic fix seems more desirable.
What matters is that the lock is held before calling device_del()
instead of being held in module_exit().
Thanks,
Ming
next prev parent reply other threads:[~2021-10-13 15:04 UTC|newest]
Thread overview: 94+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-27 16:37 [PATCH v8 00/12] syfs: generic deadlock fix with module removal Luis Chamberlain
2021-09-27 16:37 ` [PATCH v8 01/12] LICENSES: Add the copyleft-next-0.3.1 license Luis Chamberlain
[not found] ` <202110050907.35FBD2A1@keescook>
[not found] ` <YWR2ZrtzChamY1y4@bombadil.infradead.org>
2021-10-11 17:57 ` Kees Cook
2021-09-27 16:37 ` [PATCH v8 02/12] testing: use the copyleft-next-0.3.1 SPDX tag Luis Chamberlain
2021-10-05 16:11 ` Kees Cook
2021-09-27 16:37 ` [PATCH v8 03/12] selftests: add tests_sysfs module Luis Chamberlain
2021-10-05 14:16 ` Greg KH
2021-10-05 16:57 ` Tim.Bird
2021-10-11 17:40 ` Luis Chamberlain
2021-10-11 17:38 ` Luis Chamberlain
2021-10-07 14:23 ` Miroslav Benes
2021-10-11 19:11 ` Luis Chamberlain
[not found] ` <202110050912.3DF681ED@keescook>
2021-10-11 19:03 ` Luis Chamberlain
2021-09-27 16:37 ` [PATCH v8 04/12] kernfs: add initial failure injection support Luis Chamberlain
2021-10-05 19:47 ` Kees Cook
2021-10-11 20:44 ` Luis Chamberlain
2021-09-27 16:37 ` [PATCH v8 05/12] test_sysfs: add support to use kernfs failure injection Luis Chamberlain
2021-10-05 19:51 ` Kees Cook
2021-10-11 20:56 ` Luis Chamberlain
2021-09-27 16:37 ` [PATCH v8 06/12] kernel/module: add documentation for try_module_get() Luis Chamberlain
2021-10-05 19:58 ` Kees Cook
2021-10-11 21:16 ` Luis Chamberlain
2021-09-27 16:38 ` [PATCH v8 07/12] fs/kernfs/symlink.c: replace S_IRWXUGO with 0777 on kernfs_create_link() Luis Chamberlain
2021-10-05 19:59 ` Kees Cook
2021-09-27 16:38 ` [PATCH v8 08/12] fs/sysfs/dir.c: replace S_IRWXU|S_IRUGO|S_IXUGO with 0755 sysfs_create_dir_ns() Luis Chamberlain
2021-10-05 16:05 ` Kees Cook
2021-09-27 16:38 ` [PATCH v8 09/12] sysfs: fix deadlock race with module removal Luis Chamberlain
2021-10-05 9:24 ` Ming Lei
2021-10-11 21:25 ` Luis Chamberlain
2021-10-12 0:20 ` Ming Lei
2021-10-12 21:18 ` Luis Chamberlain
2021-10-13 1:07 ` Ming Lei
2021-10-13 12:35 ` Luis Chamberlain
2021-10-13 15:04 ` Ming Lei [this message]
2021-10-13 21:16 ` Luis Chamberlain
2021-10-05 20:50 ` Kees Cook
2021-10-11 22:26 ` Luis Chamberlain
2021-10-13 12:41 ` Luis Chamberlain
2021-09-27 16:38 ` [PATCH v8 10/12] test_sysfs: enable deadlock tests by default Luis Chamberlain
2021-09-27 16:38 ` [PATCH v8 11/12] zram: fix crashes with cpu hotplug multistate Luis Chamberlain
2021-10-05 20:55 ` Kees Cook
2021-10-11 18:27 ` Luis Chamberlain
2021-10-14 1:55 ` Ming Lei
2021-10-14 2:11 ` Ming Lei
2021-10-14 20:24 ` Luis Chamberlain
2021-10-14 23:52 ` Ming Lei
2021-10-15 0:22 ` Luis Chamberlain
2021-10-15 8:36 ` Ming Lei
2021-10-15 8:52 ` Greg KH
2021-10-15 17:31 ` Luis Chamberlain
2021-10-16 11:28 ` Ming Lei
2021-10-18 19:32 ` Luis Chamberlain
2021-10-19 2:34 ` Ming Lei
2021-10-19 6:23 ` Miroslav Benes
2021-10-19 9:23 ` Ming Lei
2021-10-20 6:43 ` Miroslav Benes
2021-10-20 7:49 ` Ming Lei
2021-10-20 8:19 ` Miroslav Benes
2021-10-20 8:28 ` Greg KH
2021-10-25 9:58 ` Miroslav Benes
2021-10-20 10:09 ` Ming Lei
2021-10-26 8:48 ` Petr Mladek
2021-10-26 15:37 ` Ming Lei
2021-10-26 17:01 ` Luis Chamberlain
2021-10-27 11:57 ` Miroslav Benes
2021-10-27 14:27 ` Luis Chamberlain
2021-11-02 15:24 ` Petr Mladek
2021-11-02 16:25 ` Luis Chamberlain
2021-11-03 0:01 ` Ming Lei
2021-11-03 12:44 ` Luis Chamberlain
2021-10-27 11:42 ` Miroslav Benes
2021-11-02 14:15 ` Petr Mladek
2021-11-02 14:51 ` Petr Mladek
2021-11-02 15:17 ` Ming Lei
2021-11-02 14:56 ` Ming Lei
2021-10-19 15:28 ` Luis Chamberlain
2021-10-19 16:29 ` Ming Lei
2021-10-19 19:36 ` Luis Chamberlain
2021-10-20 1:15 ` Ming Lei
2021-10-20 15:48 ` Luis Chamberlain
2021-10-21 0:39 ` Ming Lei
2021-10-21 17:18 ` Luis Chamberlain
2021-10-22 0:05 ` Ming Lei
2021-10-19 15:50 ` Luis Chamberlain
2021-10-19 16:25 ` Greg KH
2021-10-19 16:30 ` Luis Chamberlain
2021-10-19 17:28 ` Greg KH
2021-10-19 19:46 ` Luis Chamberlain
2021-10-19 16:39 ` Ming Lei
2021-10-19 19:38 ` Luis Chamberlain
2021-10-20 0:55 ` Ming Lei
2021-09-27 16:38 ` [PATCH v8 12/12] zram: use ATTRIBUTE_GROUPS to fix sysfs deadlock module removal Luis Chamberlain
2021-10-05 20:57 ` Kees Cook
2021-10-11 18:28 ` Luis Chamberlain
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