Re: [PATCH 3.18 0/1] dm: remove duplicate dm_get_live_table() in __dm_destroy()

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On Sun, Nov 11, 2018 at 02:06:54AM -0600, Corey Wright wrote:
The recently released stable version 3.18.125 introduced a deadlock
because dm_get_live_table() is called twice within __dm_destroy().

The backported commit e1db66a5 "dm: fix AB-BA deadlock in
__dm_destroy()" doesn't *move* the dm_get_live_table() call from
before the mutex_lock(), as the original commit 2a708cff does, but
instead *adds* a new dm_get_live_table() call after the mutex_lock().
The two dm_get_live_table() calls result in a deadlock:

[  311.291323] INFO: task cryptsetup:209 blocked for more than 120 seconds.
[  311.420925]       Not tainted 3.18.125+1-amd64 #1
[  311.559858] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[  311.651116] cryptsetup      D 0000000000000000     0   209    203 0x00000000
[  311.732304]  ffff88007abfd5f0 0000000000000082 0000000000000001 ffff88007a470390
[  311.873420]  00000000000136c0 ffff88007a78bfd8 00000000000136c0 ffff88007abfd5f0
[  311.934275]  0000000000000001 ffff88007a78bc70 7fffffffffffffff ffff88007a78bc68
[  311.940115] Call Trace:
[  311.949956]  [<ffffffffa01d0b70>] ? dev_suspend+0x260/0x260 [dm_mod]
[  312.179891]  [<ffffffff81553d8a>] ? schedule_timeout+0x24a/0x2d0
[  312.375447]  [<ffffffff810a7ba4>] ? __wake_up+0x34/0x50
[  312.377825]  [<ffffffff810c3374>] ? srcu_readers_seq_idx.isra.8+0x54/0x70
[  312.557921]  [<ffffffff815519b0>] ? wait_for_completion+0xb0/0x120
[  312.561314]  [<ffffffff81096340>] ? wake_up_state+0x20/0x20
[  312.664457]  [<ffffffff810c36e8>] ? __synchronize_srcu+0xd8/0x120
[  312.768794]  [<ffffffff810c3260>] ? call_srcu+0x70/0x70
[  312.790337]  [<ffffffffa01ca757>] ? __dm_destroy+0x107/0x2e0 [dm_mod]
[  312.909878]  [<ffffffffa01d0b70>] ? dev_suspend+0x260/0x260 [dm_mod]
[  312.978804]  [<ffffffffa01d0c4e>] ? dev_remove+0xde/0x120 [dm_mod]
[  313.082322]  [<ffffffffa01d12e3>] ? ctl_ioctl+0x203/0x4c0 [dm_mod]
[  313.175957]  [<ffffffffa01d15b3>] ? dm_ctl_ioctl+0x13/0x20 [dm_mod]
[  313.301981]  [<ffffffff811d40c0>] ? do_vfs_ioctl+0x2d0/0x4a0
[  313.384648]  [<ffffffff8108848c>] ? task_work_run+0xbc/0xf0
[  313.489669]  [<ffffffff811d4311>] ? SyS_ioctl+0x81/0xa0
[  313.510846]  [<ffffffff815551cd>] ? system_call_fastpath+0x16/0x1b

Removing the original dm_get_live_table() call from before the
mutex_lock() prevents the deadlock.

Thanks for maintaining 3.18!

PS Greg, Was this a subtle attempt to get someone to speak up and say
  "I am using this!" as you requested in the 3.18.125 release
  announcement? ;)

Hm, interesting. It looks like git did the wrong thing here, sorry for
that :(

--
Thanks,
Sasha



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