On 2023-10-03 00:48, Song Liu wrote:
> CC Logan.
>
> On Mon, Oct 2, 2023 at 12:22 PM John Pittman <jpittman@xxxxxxxxxx> wrote:
>>
>> Thanks a lot David. Song, as a note, David's patch was tested by a
>> Red Hat customer and it indeed resolved their hit on the deadlock.
>> cc. Laurence Oberman who assisted on that case.
>>
>>
>> On Mon, Oct 2, 2023 at 2:39 PM David Jeffery <djeffery@xxxxxxxxxx> wrote:
>>>
>>> When raid5_get_active_stripe is called with a ctx containing a stripe_head in
>>> its batch_last pointer, it can cause a deadlock if the task sleeps waiting on
>>> another stripe_head to become available. The stripe_head held by batch_last
>>> can be blocking the advancement of other stripe_heads, leading to no
>>> stripe_heads being released so raid5_get_active_stripe waits forever.
>>>
>>> Like with the quiesce state handling earlier in the function, batch_last
>>> needs to be released by raid5_get_active_stripe before it waits for another
>>> stripe_head.
>>>
>>>
>>> Fixes: 3312e6c887fe ("md/raid5: Keep a reference to last stripe_head for batch")
>>> Signed-off-by: David Jeffery <djeffery@xxxxxxxxxx>
This makes sense to me. Nice catch on the difficult bug.
Reviewed-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Logan
