From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Jens Axboe <axboe@kernel.dk>,
Andrew Morton <akpm@linux-foundation.org>,
Kay Sievers <kay.sievers@vrfy.org>,
Namhyung Kim <namhyung@gmail.com>,
Lukas Czerner <lczerner@redhat.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] loop: fput() called in loop_clr_fd() may cause bd_mutex recursive locking
Date: Sun, 18 Dec 2011 01:19:28 +0300 [thread overview]
Message-ID: <20111217221928.GB3313@swordfish> (raw)
In-Reply-To: <20111217221232.GA2203@ZenIV.linux.org.uk>
On (12/17/11 22:12), Al Viro wrote:
> >
> > [23044.654647] umount/24442 is trying to acquire lock:
> > [23044.654652] (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff81144311>] blkdev_put+0x1f/0x131
> > [23044.654670]
> > [23044.654672] but task is already holding lock:
> > [23044.654677] (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff811441a1>] __blkdev_put+0x33/0x184
> > [23044.654690]
> > [23044.654692] other info that might help us debug this:
> > [23044.654697] Possible unsafe locking scenario:
> > [23044.654727]
> > [23044.654731] 1 lock held by umount/24442:
> > [23044.654735] #0: (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff811441a1>] __blkdev_put+0x33/0x184
> > [23044.654748]
> > [23044.654762] Call Trace:
> > [23044.654773] [<ffffffff81075611>] __lock_acquire+0x15bf/0x1659
> > [23044.654784] [<ffffffff8114b3e3>] ? inotify_free_group_priv+0x4f/0x4f
> > [23044.654792] [<ffffffff81144311>] ? blkdev_put+0x1f/0x131
> > [23044.654799] [<ffffffff81075c6a>] lock_acquire+0x138/0x1b3
> > [23044.654807] [<ffffffff81144311>] ? blkdev_put+0x1f/0x131
> > [23044.654814] [<ffffffff81144311>] ? blkdev_put+0x1f/0x131
> > [23044.654824] [<ffffffff8147ce67>] mutex_lock_nested+0x5e/0x325
> > [23044.654831] [<ffffffff81144311>] ? blkdev_put+0x1f/0x131
> > [23044.654838] [<ffffffff81149963>] ? fsnotify+0x441/0x459
> > [23044.654846] [<ffffffff81144311>] blkdev_put+0x1f/0x131
> > [23044.654853] [<ffffffff81144443>] blkdev_close+0x20/0x22
> > [23044.654863] [<ffffffff81116b21>] fput+0x117/0x1cf
> > [23044.654874] [<ffffffffa016eb71>] loop_clr_fd+0x1f2/0x201 [loop]
> > [23044.654882] [<ffffffffa016f861>] lo_release+0x40/0x6f [loop]
> > [23044.654890] [<ffffffff81144244>] __blkdev_put+0xd6/0x184
> > [23044.654898] [<ffffffff8114441a>] blkdev_put+0x128/0x131
> > [23044.654906] [<ffffffff8111704e>] kill_block_super+0x60/0x65
> > [23044.654914] [<ffffffff81117366>] deactivate_locked_super+0x32/0x63
> > [23044.654922] [<ffffffff81117cc9>] deactivate_super+0x3a/0x3e
> > [23044.654931] [<ffffffff8112fc5d>] mntput_no_expire+0xbf/0xc4
> > [23044.654939] [<ffffffff811309c7>] sys_umount+0x2c5/0x2f3
> > [23044.654949] [<ffffffff81484b12>] system_call_fastpath+0x16/0x1b
[..]
>
> NAK - you've "fixed" a false positive from lock checker by failing to close
> the underlying device.
>
Sorry, why is that a false positive?
blkdev_put() calls lo_release() while holding bd_mutex,
lo_release() calls loop_clr_fd() -> fput(). fput() once again
attempts to grub already held bd_mutex calling blkdev_put().
Looks like a recursion to me.
Sergey
next prev parent reply other threads:[~2011-12-17 22:22 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-17 21:53 [PATCH] loop: fput() called in loop_clr_fd() may cause bd_mutex recursive locking Sergey Senozhatsky
2011-12-17 22:12 ` Al Viro
2011-12-17 22:19 ` Sergey Senozhatsky [this message]
2011-12-17 22:30 ` Al Viro
2011-12-17 22:37 ` Sergey Senozhatsky
2011-12-17 22:58 ` Al Viro
2011-12-17 23:20 ` Sergey Senozhatsky
2011-12-17 23:38 ` Al Viro
2011-12-17 23:47 ` Sergey Senozhatsky
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