Re: block: cover another queue enter recursion via BIO_QUEUE_ENTERED

[Mike Snitzer <snitzer@redhat.com>]

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>