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Subject[regression] v3.8 -> v3.9-rc6, caused by commit 8761a3d ("loop: cleanup partitions when detaching loop device")
Date
Hello,

the following simple test causes a deadlock between the loop driver,
umount and blkid i v3.9-rc6 (tested on a standard Debian wheezy
installating, i.e. with udev 175):

qmitest:~# file cd-image-cfg1.iso
cd-image-cfg1.iso: # ISO 9660 CD-ROM filesystem data 'D-LINK MODEM'
qmitest:~# mount cd-image-cfg1.iso /mnt/ -oloop,ro -t iso9660
qmitest:~# umount /mnt


where umount will hang forever.


[ 241.456242] INFO: task umount:2579 blocked for more than 120 seconds.
[ 241.467141] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 241.481152] umount D 0000000000000000 0 2579 2526 0x00000000
[ 241.494602] ffff88000ef37c58 0000000000000046 ffff88000d8af040 ffff88000ef36010
[ 241.509897] ffff88000ef36000 ffff88000ef36000 ffff88000ef36000 ffff88000ef37fd8
[ 241.525433] 0000000000013180 ffff88000ef36000 ffffffff81811400 ffff88000d8af040
[ 241.540846] Call Trace:
[ 241.545642] [<ffffffff813ba434>] schedule+0x5f/0x61
[ 241.554326] [<ffffffff813ba6b5>] schedule_preempt_disabled+0x21/0x29
[ 241.568270] [<ffffffff813b8ff7>] __mutex_lock_common+0x26a/0x3b9
[ 241.580711] [<ffffffffa02bbd37>] ? loop_clr_fd+0x20d/0x279 [loop]
[ 241.593127] [<ffffffff8107f71d>] ? mark_held_locks+0x73/0x97
[ 241.604733] [<ffffffffa02bbd37>] ? loop_clr_fd+0x20d/0x279 [loop]
[ 241.617167] [<ffffffff813b9241>] mutex_lock_nested+0x3b/0x40
[ 241.628775] [<ffffffffa02bbd37>] loop_clr_fd+0x20d/0x279 [loop]
[ 241.640876] [<ffffffffa02bc4b5>] lo_release+0x40/0x6a [loop]
[ 241.652573] [<ffffffff811476a3>] __blkdev_put+0xb5/0x168
[ 241.664783] [<ffffffff8114787d>] blkdev_put+0x127/0x130
[ 241.676804] [<ffffffff8111b48d>] kill_block_super+0x5f/0x64
[ 241.689433] [<ffffffff8111b6b5>] deactivate_locked_super+0x21/0x4d
[ 241.703484] [<ffffffff8111c26c>] deactivate_super+0x40/0x48
[ 241.721619] [<ffffffff811325fd>] mntput_no_expire+0x12d/0x136
[ 241.734652] [<ffffffff811334e0>] sys_umount+0x33e/0x369
[ 241.746746] [<ffffffff81046f28>] ? __set_current_blocked+0x26/0x49
[ 241.760553] [<ffffffff813bc2e9>] system_call_fastpath+0x16/0x1b
[ 241.773833] 2 locks held by umount/2579:
[ 241.783138] #0: (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff81147621>] __blkdev_put+0x33/0x168
[ 241.805858] #1: (&bdev->bd_mutex/1){+.+...}, at: [<ffffffffa02bbd37>] loop_clr_fd+0x20d/0x279 [loop]
[ 241.830869] INFO: task blkid:2580 blocked for more than 120 seconds.
[ 241.844648] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 241.862451] blkid D 0000000000000001 0 2580 442 0x00000004
[ 241.879441] ffff88000db55a48 0000000000000046 ffffffff818548e0 ffff88000db54010
[ 241.900248] ffff88000db54000 ffff88000db54000 ffff88000db54000 ffff88000db55fd8
[ 241.920555] 0000000000013180 ffff88000db54000 ffff88000ecae040 ffff88000db69040
[ 241.940945] Call Trace:
[ 241.947643] [<ffffffff813ba434>] schedule+0x5f/0x61
[ 241.958943] [<ffffffff813ba6b5>] schedule_preempt_disabled+0x21/0x29
[ 241.973093] [<ffffffff813b8ff7>] __mutex_lock_common+0x26a/0x3b9
[ 241.986524] [<ffffffff81147956>] ? __blkdev_get+0xaf/0x3f7
[ 241.999026] [<ffffffff81147956>] ? __blkdev_get+0xaf/0x3f7
[ 242.011487] [<ffffffff813b9241>] mutex_lock_nested+0x3b/0x40
[ 242.030079] [<ffffffff81147956>] __blkdev_get+0xaf/0x3f7
[ 242.042256] [<ffffffff81147fec>] ? blkdev_get+0x34e/0x34e
[ 242.054748] [<ffffffff81147eac>] blkdev_get+0x20e/0x34e
[ 242.067038] [<ffffffff81147fec>] ? blkdev_get+0x34e/0x34e
[ 242.079440] [<ffffffff813bb66e>] ? _raw_spin_unlock+0x26/0x3a
[ 242.093235] [<ffffffff81147fec>] ? blkdev_get+0x34e/0x34e
[ 242.105630] [<ffffffff81148055>] blkdev_open+0x69/0x6d
[ 242.117541] [<ffffffff811178f8>] do_dentry_open+0x16c/0x21e
[ 242.130485] [<ffffffff81117a8a>] finish_open+0x34/0x40
[ 242.142334] [<ffffffff81123f77>] do_last+0x898/0xa46
[ 242.153893] [<ffffffff81124180>] ? link_path_walk+0x5b/0x432
[ 242.166726] [<ffffffff8112318c>] ? path_init+0xcd/0x2b6
[ 242.178852] [<ffffffff811246a5>] path_openat+0xc6/0x374
[ 242.190816] [<ffffffff81124a58>] do_filp_open+0x38/0x84
[ 242.202779] [<ffffffff813bb66e>] ? _raw_spin_unlock+0x26/0x3a
[ 242.215780] [<ffffffff81130182>] ? __alloc_fd+0x106/0x11a
[ 242.228092] [<ffffffff81117640>] do_sys_open+0x6d/0xff
[ 242.239965] [<ffffffff811176ff>] sys_open+0x1c/0x1e
[ 242.251195] [<ffffffff813bc2e9>] system_call_fastpath+0x16/0x1b
[ 242.264583] 1 lock held by blkid/2580:
[ 242.273704] #0: (&bdev->bd_mutex){+.+.+.}, at: [<ffffffff81147956>] __blkdev_get+0xaf/0x3f7


Reverting commit 8761a3d ("loop: cleanup partitions when detaching loop
device") on top of v3.9-rc9 fixes this problem for me.



Bjørn
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