[dm-devel] [PATCH V2] md: don't unregister sync_thread with reconfig_mutex held

[Guoqing Jiang]

On 12/9/21 8:57 PM, Donald Buczek wrote:
> [Update Guoqing’s email address]
>
> On 15.02.21 12:07, Paul Menzel wrote:
>> [+cc Donald]
>>
>> Am 13.02.21 um 01:49 schrieb Guoqing Jiang:
>>> Unregister sync_thread doesn't need to hold reconfig_mutex since it
>>> doesn't reconfigure array.
>>>
>>> And it could cause deadlock problem for raid5 as follows:
>>>
>>> 1. process A tried to reap sync thread with reconfig_mutex held 
>>> after echo
>>>     idle to sync_action.
>>> 2. raid5 sync thread was blocked if there were too many active stripes.
>>> 3. SB_CHANGE_PENDING was set (because of write IO comes from upper 
>>> layer)
>>>     which causes the number of active stripes can't be decreased.
>>> 4. SB_CHANGE_PENDING can't be cleared since md_check_recovery was 
>>> not able
>>>     to hold reconfig_mutex.
>>>
>>> More details in the link:
>>> https://lore.kernel.org/linux-raid/5ed54ffc-ce82-bf66-4eff-390cb23bc1ac@molgen.mpg.de/T/#t 
>>>
>>>
>>> And add one parameter to md_reap_sync_thread since it could be 
>>> called by
>>> dm-raid which doesn't hold reconfig_mutex.
>>>
>>> Reported-and-tested-by: Donald Buczek <buczek at molgen.mpg.de>
>
> Thanks, Paul, for putting me into the cc.
>
> Guoqing, I don't think, I've tested this patch. Please remove the 
> tested-by.

This version is basically the similar as the change in the thread.

https://lore.kernel.org/linux-raid/5ed54ffc-ce82-bf66-4eff-390cb23bc1ac@molgen.mpg.de/T/#m546d8c55a42f308985b9d31d4be85832edcd15ab

Anyway, I will remove your tested-by per the request if I will update 
the patch.

Thanks,
Guoqing