Messages in this thread | | | Date | Sun, 18 Dec 2011 01:19:28 +0300 | From | Sergey Senozhatsky <> | Subject | Re: [PATCH] loop: fput() called in loop_clr_fd() may cause bd_mutex recursive locking |
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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
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