From: Luis Chamberlain <mcgrof@kernel.org>
To: Bart Van Assche <bvanassche@acm.org>
Cc: tj@kernel.org, gregkh@linuxfoundation.org,
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Subject: Re: [PATCH v7 09/12] sysfs: fix deadlock race with module removal
Date: Mon, 20 Sep 2021 14:43:45 -0700 [thread overview]
Message-ID: <YUkAkSUQtUZvNvTu@bombadil.infradead.org> (raw)
In-Reply-To: <6db06c27-e3af-b0aa-6f38-9c31dd8194fa@acm.org>
On Mon, Sep 20, 2021 at 02:36:38PM -0700, Bart Van Assche wrote:
> On 9/17/21 10:04 PM, Luis Chamberlain wrote:
> > A sketch of how this can happen follows:
> >
> > CPU A CPU B
> > whatever_store()
> > module_unload
> > mutex_lock(foo)
> > mutex_lock(foo)
> > del_gendisk(zram->disk);
> > device_del()
> > device_remove_groups()
> >
> > In this situation whatever_store() is waiting for the mutex foo to
> > become unlocked, but that won't happen until module removal is complete.
> > But module removal won't complete until the sysfs file being poked
> > completes which is waiting for a lock already held.
>
> If I remember correctly I encountered the deadlock scenario described
> above for the first time about ten years ago while working on the SCST
> project. We solved this deadlock by removing the sysfs attributes from
> the module unload code before grabbing mutex_lock(foo), e.g. by calling
> sysfs_remove_file().
Well the sysfs attributes in zram do tons of funky mucking around so
unfortunately no. It's not the only driver where this can happen. It is
why I decided to work on a generic solution instead.
> This works because calling sysfs_remove_file()
> multiple times in a row is safe. Is that solution good enough for the
> zram driver?
The sysfs attributes are group attributes part of the block, and so are
removed for the driver on a del_gendisk(). So unfortunately no, this
would not be a good solution in this case.
Luis
next prev parent reply other threads:[~2021-09-21 1:43 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20210918050430.3671227-1-mcgrof@kernel.org>
2021-09-18 5:04 ` [PATCH v7 01/12] LICENSES: Add the copyleft-next-0.3.1 license Luis Chamberlain
2021-09-18 5:04 ` [PATCH v7 02/12] testing: use the copyleft-next-0.3.1 SPDX tag Luis Chamberlain
2021-09-18 5:04 ` [PATCH v7 03/12] selftests: add tests_sysfs module Luis Chamberlain
2021-09-20 21:38 ` Bart Van Assche
2021-09-18 5:04 ` [PATCH v7 04/12] kernfs: add initial failure injection support Luis Chamberlain
2021-09-18 5:04 ` [PATCH v7 05/12] test_sysfs: add support to use kernfs failure injection Luis Chamberlain
2021-09-18 5:04 ` [PATCH v7 06/12] kernel/module: add documentation for try_module_get() Luis Chamberlain
2021-09-18 5:04 ` [PATCH v7 07/12] fs/kernfs/symlink.c: replace S_IRWXUGO with 0777 on kernfs_create_link() Luis Chamberlain
2021-09-18 5:04 ` [PATCH v7 08/12] fs/sysfs/dir.c: replace S_IRWXU|S_IRUGO|S_IXUGO with 0755 sysfs_create_dir_ns() Luis Chamberlain
2021-09-18 5:04 ` [PATCH v7 09/12] sysfs: fix deadlock race with module removal Luis Chamberlain
2021-09-20 17:53 ` Tejun Heo
2021-09-20 19:15 ` Luis Chamberlain
2021-09-20 19:22 ` Tejun Heo
2021-09-20 19:38 ` Luis Chamberlain
2021-09-20 20:52 ` Dan Williams
2021-09-20 21:17 ` Luis Chamberlain
2021-09-20 21:55 ` Dan Williams
2021-09-21 0:03 ` Luis Chamberlain
2021-09-20 21:36 ` Bart Van Assche
2021-09-20 21:43 ` Luis Chamberlain [this message]
2021-09-18 5:04 ` [PATCH v7 10/12] test_sysfs: enable deadlock tests by default Luis Chamberlain
2021-09-18 5:04 ` [PATCH v7 11/12] zram: fix crashes with cpu hotplug multistate Luis Chamberlain
2021-09-18 5:04 ` [PATCH v7 12/12] zram: use ATTRIBUTE_GROUPS to fix sysfs deadlock module removal Luis Chamberlain
2021-09-20 17:55 ` [PATCH v7 00/12 (RESEND)] syfs: generic deadlock fix with " Tejun Heo
2021-09-27 15:11 ` Luis Chamberlain
[not found] <20210917194709.3562413-1-mcgrof@kernel.org>
[not found] ` <20210917194709.3562413-10-mcgrof@kernel.org>
[not found] ` <c70dcb03e27e43c5b5311e184357df39@AcuMS.aculab.com>
2021-09-21 15:48 ` [PATCH v7 09/12] sysfs: fix deadlock race " Luis Chamberlain
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