On 01/08/18 20:15, 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);
So I've had v3 running fine with 4.14++ and when I first tried Jens'
additional helpers on top, I got a bunch of warnings which I didn't
investigate further at the time. Now they are back since the helpers
moved into patch #1 and #2 correctly says:
..
block/blk-mq.c: In function ‘blk_mq_complete_request’:
./include/linux/srcu.h:175:2: warning: ‘srcu_idx’ may be used uninitialized in this function [-Wmaybe-uninitialized]
__srcu_read_unlock(sp, idx);
^~~~~~~~~~~~~~~~~~~~~~~~~~~
block/blk-mq.c:587:6: note: ‘srcu_idx’ was declared here
int srcu_idx;
^~~~~~~~
..etc.
This is with gcc 7.2.0.
I understand that this is a somewhat-false positive since the lock always
precedes the unlock & writes to the value, but can we properly initialize
or annotate this?
cheers
Holger
