On Wed, Apr 03, 2019 at 01:11:26PM -0700, Bart Van Assche wrote:
If blk_mq_try_issue_directly() returns BLK_STS*_RESOURCE that means that the request has not been queued and that the caller should retry to submit the request. Both blk_mq_request_bypass_insert() and blk_mq_sched_insert_request() guarantee that a request will be processed. Hence return BLK_STS_OK if one of these functions is called. This patch avoids that blk_mq_dispatch_rq_list() crashes when using dm-mpath.
Cc: Christoph Hellwig hch@infradead.org Cc: Hannes Reinecke hare@suse.com Cc: James Smart james.smart@broadcom.com Cc: Ming Lei ming.lei@redhat.com Cc: Jianchao Wang jianchao.w.wang@oracle.com Cc: Keith Busch keith.busch@intel.com Cc: Dongli Zhang dongli.zhang@oracle.com Cc: Laurence Oberman loberman@redhat.com Tested-by: Laurence Oberman loberman@redhat.com Reviewed-by: Laurence Oberman loberman@redhat.com Reported-by: Laurence Oberman loberman@redhat.com Fixes: 7f556a44e61d ("blk-mq: refactor the code of issue request directly") # v5.0. Cc: stable@vger.kernel.org Signed-off-by: Bart Van Assche bvanassche@acm.org
block/blk-mq.c | 9 ++------- 1 file changed, 2 insertions(+), 7 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c index 652d0c6d5945..b2c20dce8a30 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1859,16 +1859,11 @@ blk_status_t blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx, case BLK_STS_RESOURCE: if (force) { blk_mq_request_bypass_insert(rq, run_queue);
/** We have to return BLK_STS_OK for the DM* to avoid livelock. Otherwise, we return* the real result to indicate whether the* request is direct-issued successfully.*/ret = bypass ? BLK_STS_OK : ret;
ret = BLK_STS_OK;ret = BLK_STS_OK;
This change itself is correct.
However, there is other issue introduced by 7f556a44e61d.
We need blk_insert_cloned_request() to pass back BLK_STS_RESOURCE/BLK_STS_RESOURCE to caller, so that dm-rq driver may see the underlying queue is busy, then tell blk-mq to deal with the busy condition from dm-rq queue, so that IO merge can get improved.
That is exactly what 396eaf21ee17c476e8f6 ("blk-mq: improve DM's blk-mq IO merging via blk_insert_cloned_request feedback") did.
There must be performance regression with 7f556a44e61d by cut the feedback.
So could you fix them all in one patch?
Thanks, Ming