Re: [PATCH V2] md: don't unregister sync_thread with reconfig_mutex held

On 12/9/21 8:57 PM, Donald Buczek wrote:

[Update Guoqing’s email address]

On 15.02.21 12:07, Paul Menzel wrote:

quoted

[+cc Donald]

Am 13.02.21 um 01:49 schrieb Guoqing Jiang:

quoted

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 (local) 


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 <redacted>

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 (local)

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

Thanks,
Guoqing