Re: block: cover another queue enter recursion via BIO_QUEUE_ENTERED

[Jens Axboe <axboe@kernel.dk>]

On 1/22/19 10:15 AM, Mike Snitzer wrote:
> On Tue, Jan 22 2019 at  3:20am -0500,
> Ming Lei <ming.lei@redhat.com> wrote:
> 
>> Except for blk_queue_split(), bio_split() is used for splitting bio too,
>> then the remained bio is often resubmit to queue via generic_make_request().
>> So the same queue enter recursion exits in this case too. Unfortunatley
>> commit cd4a4ae4683dc2 doesn't help this case.
>>
>> This patch covers the above case by setting BIO_QUEUE_ENTERED before calling
>> q->make_request_fn.
>>
>> In theory the per-bio flag is used to simulate one stack variable, it is
>> just fine to clear it after q->make_request_fn is returned. Especially
>> the same bio can't be submitted from another context.
>>
>> Fixes: cd4a4ae4683dc2 ("block: don't use blocking queue entered for recursive bio submits")
>> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
>> Cc: Mike Snitzer <snitzer@redhat.com>
>> Cc: NeilBrown <neilb@suse.com>
>> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> 
> Looks good, I'll drop my DM patch that set/cleared BIO_QUEUE_ENTERED.
> 
> Jens, you OK with picking this up for 5.0-rc?
> 
> Reviewed-by:  Mike Snitzer <snitzer@redhat.com>

I am, thanks both of you for looking into this. I'm a bit behind on email
and patches from over the long weekend.

-- 
Jens Axboe