Re: [PATCH 2/2] block: free merged request in the caller

[Omar Sandoval <osandov@osandov.com>]

On Thu, Feb 02, 2017 at 09:06:13AM -0700, Jens Axboe wrote:
> If we end up doing a request-to-request merge when we have completed
> a bio-to-request merge, we free the request from deep down in that
> path. For blk-mq-sched, the merge path has to hold the appropriate
> lock, but we don't need it for freeing the request. And in fact
> holding the lock is problematic, since we are now calling the
> mq sched put_rq_private() hook with the lock held. Other call paths
> do not hold this lock.
> 
> Fix this inconsistency by ensuring that the caller frees a merged
> request. Then we can do it outside of the lock, making it both more
> efficient and fixing the blk-mq-sched problem of invoking parts of
> the scheduler with an unknown lock state.
> 
> Reported-by: Paolo Valente <paolo.valente@linaro.org>

Reviewed-by: Omar Sandoval <osandov@fb.com>

> Signed-off-by: Jens Axboe <axboe@fb.com>
> ---
>  block/blk-core.c     | 12 +++++++++---
>  block/blk-merge.c    | 15 ++++++++++++---
>  block/blk-mq-sched.c |  9 ++++++---
>  block/blk-mq-sched.h |  3 ++-
>  block/mq-deadline.c  |  8 ++++++--
>  5 files changed, 35 insertions(+), 12 deletions(-)