Fix two places in commit 104655fd4d ("dm thin: support discards") that
didn't use pool->lock to protect against concurrent changes to the
prepared_discards list.
Without this fix, thin_endio() can race with process_discard(), leading
to concurrent list_add()s that result in the processes locking up with
an error like the following:
WARNING: at lib/list_debug.c:32 __list_add+0x8f/0xa0()
...
list_add corruption. next->prev should be prev (ffff880323b96140), but was ffff8801d2c48440. (next=ffff8801d2c485c0).
...
Pid: 17205, comm: kworker/u:1 Tainted: G W O 3.4.0-rc3.snitm+ #1
Call Trace:
[<ffffffff8103ca1f>] warn_slowpath_common+0x7f/0xc0
[<ffffffff8103cb16>] warn_slowpath_fmt+0x46/0x50
[<ffffffffa04f6ce6>] ? bio_detain+0xc6/0x210 [dm_thin_pool]
[<ffffffff8124ff3f>] __list_add+0x8f/0xa0
[<ffffffffa04f70d2>] process_discard+0x2a2/0x2d0 [dm_thin_pool]
[<ffffffffa04f6a78>] ? remap_and_issue+0x38/0x50 [dm_thin_pool]
[<ffffffffa04f7c3b>] process_deferred_bios+0x7b/0x230 [dm_thin_pool]
[<ffffffffa04f7df0>] ? process_deferred_bios+0x230/0x230 [dm_thin_pool]
[<ffffffffa04f7e42>] do_worker+0x52/0x60 [dm_thin_pool]
[<ffffffff81056fa9>] process_one_work+0x129/0x450
[<ffffffff81059b9c>] worker_thread+0x17c/0x3c0
[<ffffffff81059a20>] ? manage_workers+0x120/0x120
[<ffffffff8105eabe>] kthread+0x9e/0xb0
[<ffffffff814ceda4>] kernel_thread_helper+0x4/0x10
[<ffffffff8105ea20>] ? kthread_freezable_should_stop+0x70/0x70
[<ffffffff814ceda0>] ? gs_change+0x13/0x13
---[ end trace 7e0a523bc5e52692 ]---
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
c3a0ce2eab