From: Jens Axboe <jaxboe@fusionio.com>
To: Kay Sievers <kay.sievers@vrfy.org>
Cc: Milan Broz <mbroz@redhat.com>, Tejun Heo <tj@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: loop: fix deadlock when sysfs and LOOP_CLR_FD race against each other
Date: Sun, 31 Jul 2011 22:20:24 +0200 [thread overview]
Message-ID: <4E35B908.6090507@fusionio.com> (raw)
In-Reply-To: <1312053553.1187.17.camel@mop>
On 2011-07-30 21:19, Kay Sievers wrote:
> From: Kay Sievers <kay.sievers@vrfy.org>
> Subject: loop: fix deadlock when sysfs and LOOP_CLR_FD race against each other
>
> LOOP_CLR_FD takes lo->lo_ctl_mutex and tries to remove the loop sysfs
> files. Sysfs calls show() and waits for lo->lo_ctl_mutex. LOOP_CLR_FD
> waits for show() to finish to remove the sysfs file.
>
> cat /sys/class/block/loop0/loop/backing_file
> mutex_lock_nested+0x176/0x350
> ? loop_attr_do_show_backing_file+0x2f/0xd0 [loop]
> ? loop_attr_do_show_backing_file+0x2f/0xd0 [loop]
> loop_attr_do_show_backing_file+0x2f/0xd0 [loop]
> dev_attr_show+0x1b/0x60
> ? sysfs_read_file+0x86/0x1a0
> ? __get_free_pages+0x12/0x50
> sysfs_read_file+0xaf/0x1a0
>
> ioctl(LOOP_CLR_FD):
> wait_for_common+0x12c/0x180
> ? try_to_wake_up+0x2a0/0x2a0
> wait_for_completion+0x18/0x20
> sysfs_deactivate+0x178/0x180
> ? sysfs_addrm_finish+0x43/0x70
> ? sysfs_addrm_start+0x1d/0x20
> sysfs_addrm_finish+0x43/0x70
> sysfs_hash_and_remove+0x85/0xa0
> sysfs_remove_group+0x59/0x100
> loop_clr_fd+0x1dc/0x3f0 [loop]
> lo_ioctl+0x223/0x7a0 [loop]
>
> Instead of taking the lo_ctl_mutex from sysfs code, take the inner
> lo->lo_lock, to protect the access to the backing_file data.
>
> Thanks to Tejun for help debugging and finding a solution.
Looks good, looks like something that should have a stable tag as well?
--
Jens Axboe
next prev parent reply other threads:[~2011-07-31 20:20 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-30 19:19 loop: fix deadlock when sysfs and LOOP_CLR_FD race against each other Kay Sievers
2011-07-31 20:20 ` Jens Axboe [this message]
2011-07-31 20:42 ` Kay Sievers
2011-07-31 20:57 ` Jens Axboe
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