Re: [PATCH] Btrfs: fix compressed write corruption on enospc

[Chris Mason <clm@fb.com>]

On 08/06/2014 11:18 AM, Chris Mason wrote:
> On 08/06/2014 10:43 AM, Martin Steigerwald wrote:
>> Am Mittwoch, 6. August 2014, 09:35:51 schrieb Chris Mason:
>>> On 08/06/2014 06:21 AM, Martin Steigerwald wrote:
>>>>> I think this should go to stable. Thanks, Liu.
>>>
>>> I'm definitely tagging this for stable.
>>>
>>>> Unfortunately this fix does not seem to fix all lockups.
>>>
>>> The traces below are a little different, could you please send the whole
>>> file?
>>
>> Will paste it at the end.
> 
> [90496.156016] kworker/u8:14   D ffff880044e38540     0 21050      2 0x00000000
> [90496.157683] Workqueue: btrfs-delalloc normal_work_helper [btrfs]
> [90496.159320]  ffff88022880f990 0000000000000002 ffff880407f649b0 ffff88022880ffd8
> [90496.160997]  ffff880044e38000 0000000000013040 ffff880044e38000 7fffffffffffffff
> [90496.162686]  ffff880301383aa0 0000000000000002 ffffffff814705d0 ffff880301383a98
> [90496.164360] Call Trace:
> [90496.166028]  [<ffffffff814705d0>] ? michael_mic.part.6+0x21/0x21
> [90496.167854]  [<ffffffff81470fd0>] schedule+0x64/0x66
> [90496.169574]  [<ffffffff814705ff>] schedule_timeout+0x2f/0x114
> [90496.171221]  [<ffffffff8106479a>] ? wake_up_process+0x2f/0x32
> [90496.172867]  [<ffffffff81062c3b>] ? get_parent_ip+0xd/0x3c
> [90496.174472]  [<ffffffff81062ce5>] ? preempt_count_add+0x7b/0x8e
> [90496.176053]  [<ffffffff814717f3>] __wait_for_common+0x11e/0x163
> [90496.177619]  [<ffffffff814717f3>] ? __wait_for_common+0x11e/0x163
> [90496.179173]  [<ffffffff810647aa>] ? wake_up_state+0xd/0xd
> [90496.180728]  [<ffffffff81471857>] wait_for_completion+0x1f/0x21
> [90496.182285]  [<ffffffffc044e3b3>] btrfs_async_run_delayed_refs+0xbf/0xd9 [btrfs]
> [90496.183833]  [<ffffffffc04624e1>] __btrfs_end_transaction+0x2b6/0x2ec [btrfs]
> [90496.185380]  [<ffffffffc0462522>] btrfs_end_transaction+0xb/0xd [btrfs]
> [90496.186940]  [<ffffffffc0451742>] find_free_extent+0x8a9/0x976 [btrfs]
> [90496.189464]  [<ffffffffc0451990>] btrfs_reserve_extent+0x6f/0x119 [btrfs]
> [90496.191326]  [<ffffffffc0466b45>] cow_file_range+0x1a6/0x377 [btrfs]
> [90496.193080]  [<ffffffffc047adc4>] ? extent_write_locked_range+0x10c/0x11e [btrfs]
> [90496.194659]  [<ffffffffc04677e4>] submit_compressed_extents+0x100/0x412 [btrfs]
> [90496.196225]  [<ffffffff8120e344>] ? debug_smp_processor_id+0x17/0x19
> [90496.197776]  [<ffffffffc0467b78>] async_cow_submit+0x82/0x87 [btrfs]
> [90496.199383]  [<ffffffffc048644b>] normal_work_helper+0x153/0x224 [btrfs]
> [90496.200944]  [<ffffffff81052d8c>] process_one_work+0x16f/0x2b8
> [90496.202483]  [<ffffffff81053636>] worker_thread+0x27b/0x32e
> [90496.204000]  [<ffffffff810533bb>] ? cancel_delayed_work_sync+0x10/0x10
> [90496.205514]  [<ffffffff81058012>] kthread+0xb2/0xba
> [90496.207040]  [<ffffffff81470000>] ? ap_handle_dropped_data+0xf/0xc8
> [90496.208565]  [<ffffffff81057f60>] ? __kthread_parkme+0x62/0x62
> [90496.210096]  [<ffffffff81473f6c>] ret_from_fork+0x7c/0xb0
> [90496.211618]  [<ffffffff81057f60>] ? __kthread_parkme+0x62/0x62
> 
> 
> Ok, this should explain the hang.  submit_compressed_extents is calling
> cow_file_range with a locked page.
> 
> cow_file_range is trying to find a free extent and in the process is
> calling btrfs_end_transaction, which is running the async delayed refs,
> which is trying to write dirty pages, which is waiting for your locked
> page.
> 
> I should be able to reproduce this ;)

This part of the trace is relatively new because Liu Bo's patch made us
redirty the pages, making it more likely that we'd try to write them
during commit.

But, at the end of the day we have a fundamental deadlock with
committing a transaction while holding a locked page from an ordered file.

For now, I'm ripping out the strict ordered file and going back to a
best-effort filemap_flush like ext4 is using.

-chris