On Mon, 2018-01-08 at 11:15 -0800, Tejun Heo wrote: > Currently, blk-mq protects only the issue path with RCU. This patch > puts the completion path under the same RCU protection. This will be > used to synchronize issue/completion against timeout by later patches, > which will also add the comments. > > Signed-off-by: Tejun Heo <tj@xxxxxxxxxx> > --- > block/blk-mq.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index ddc9261..6741c3e 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -584,11 +584,16 @@ static void hctx_lock(struct blk_mq_hw_ctx *hctx, int *srcu_idx) > void blk_mq_complete_request(struct request *rq) > { > struct request_queue *q = rq->q; > + struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, rq->mq_ctx->cpu); > + int srcu_idx; > > if (unlikely(blk_should_fake_timeout(q))) > return; > + > + hctx_lock(hctx, &srcu_idx); > if (!blk_mark_rq_complete(rq)) > __blk_mq_complete_request(rq); > + hctx_unlock(hctx, srcu_idx); > } > EXPORT_SYMBOL(blk_mq_complete_request); Hello Tejun, I'm concerned about the additional CPU cycles needed for the new blk_mq_map_queue() call, although I know this call is cheap. Would the timeout code really get that much more complicated if the hctx_lock() and hctx_unlock() calls would be changed into rcu_read_lock() and rcu_read_unlock() calls? Would it be sufficient if "if (has_rcu) synchronize_rcu();" would be changed into "synchronize_rcu();" in blk_mq_timeout_work()? Thanks, Bart.