| Message ID | 20201130101921.52754-1-dwagner@suse.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] blk-mq: Remove 'running from the wrong CPU' warning | expand |
On Mon, Nov 30, 2020 at 11:19:21AM +0100, Daniel Wagner wrote: > It's guaranteed that no request is in flight when a hctx is going > offline. This warning is only triggered when the wq's CPU is hot > plugged and the blk-mq is not synced up yet. > > As this state is temporary and the request is still processed > correctly, better remove the warning as this is the fast path. > > Suggested-by: Ming Lei <ming.lei@redhat.com> > Signed-off-by: Daniel Wagner <dwagner@suse.de> Looks good, Reviewed-by: Christoph Hellwig <hch@lst.de>
On Mon, Nov 30, 2020 at 11:19:21AM +0100, Daniel Wagner wrote: > It's guaranteed that no request is in flight when a hctx is going > offline. This warning is only triggered when the wq's CPU is hot > plugged and the blk-mq is not synced up yet. > > As this state is temporary and the request is still processed > correctly, better remove the warning as this is the fast path. > > Suggested-by: Ming Lei <ming.lei@redhat.com> > Signed-off-by: Daniel Wagner <dwagner@suse.de> > --- > > v2: > - remove the warning as suggested by Ming > v1: > - initial version > https://lore.kernel.org/linux-block/20201126095152.19151-1-dwagner@suse.de/ > > block/blk-mq.c | 25 ------------------------- > 1 file changed, 25 deletions(-) > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 55bcee5dc032..7e6761804f86 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -1495,31 +1495,6 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx) > { > int srcu_idx; > > - /* > - * We should be running this queue from one of the CPUs that > - * are mapped to it. > - * > - * There are at least two related races now between setting > - * hctx->next_cpu from blk_mq_hctx_next_cpu() and running > - * __blk_mq_run_hw_queue(): > - * > - * - hctx->next_cpu is found offline in blk_mq_hctx_next_cpu(), > - * but later it becomes online, then this warning is harmless > - * at all > - * > - * - hctx->next_cpu is found online in blk_mq_hctx_next_cpu(), > - * but later it becomes offline, then the warning can't be > - * triggered, and we depend on blk-mq timeout handler to > - * handle dispatched requests to this hctx > - */ > - if (!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask) && > - cpu_online(hctx->next_cpu)) { > - printk(KERN_WARNING "run queue from wrong CPU %d, hctx %s\n", > - raw_smp_processor_id(), > - cpumask_empty(hctx->cpumask) ? "inactive": "active"); > - dump_stack(); > - } > - > /* > * We can't run the queue inline with ints disabled. Ensure that > * we catch bad users of this early. > -- > 2.16.4 > Reviewed-by: Ming Lei <ming.lei@redhat.com> Thanks, Ming
On Mon, Nov 30, 2020 at 05:17:48PM +0000, Christoph Hellwig wrote: > On Mon, Nov 30, 2020 at 11:19:21AM +0100, Daniel Wagner wrote: > > It's guaranteed that no request is in flight when a hctx is going > > offline. This warning is only triggered when the wq's CPU is hot > > plugged and the blk-mq is not synced up yet. > > > > As this state is temporary and the request is still processed > > correctly, better remove the warning as this is the fast path. > > > > Suggested-by: Ming Lei <ming.lei@redhat.com> > > Signed-off-by: Daniel Wagner <dwagner@suse.de> > > Looks good, > > Reviewed-by: Christoph Hellwig <hch@lst.de> Jens, any chance you queue this one up? Thanks, Daniel
On 11/30/20 3:19 AM, Daniel Wagner wrote: > It's guaranteed that no request is in flight when a hctx is going > offline. This warning is only triggered when the wq's CPU is hot > plugged and the blk-mq is not synced up yet. > > As this state is temporary and the request is still processed > correctly, better remove the warning as this is the fast path. Applied, thanks.
diff --git a/block/blk-mq.c b/block/blk-mq.c index 55bcee5dc032..7e6761804f86 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1495,31 +1495,6 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx) { int srcu_idx; - /* - * We should be running this queue from one of the CPUs that - * are mapped to it. - * - * There are at least two related races now between setting - * hctx->next_cpu from blk_mq_hctx_next_cpu() and running - * __blk_mq_run_hw_queue(): - * - * - hctx->next_cpu is found offline in blk_mq_hctx_next_cpu(), - * but later it becomes online, then this warning is harmless - * at all - * - * - hctx->next_cpu is found online in blk_mq_hctx_next_cpu(), - * but later it becomes offline, then the warning can't be - * triggered, and we depend on blk-mq timeout handler to - * handle dispatched requests to this hctx - */ - if (!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask) && - cpu_online(hctx->next_cpu)) { - printk(KERN_WARNING "run queue from wrong CPU %d, hctx %s\n", - raw_smp_processor_id(), - cpumask_empty(hctx->cpumask) ? "inactive": "active"); - dump_stack(); - } - /* * We can't run the queue inline with ints disabled. Ensure that * we catch bad users of this early.
It's guaranteed that no request is in flight when a hctx is going offline. This warning is only triggered when the wq's CPU is hot plugged and the blk-mq is not synced up yet. As this state is temporary and the request is still processed correctly, better remove the warning as this is the fast path. Suggested-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Daniel Wagner <dwagner@suse.de> --- v2: - remove the warning as suggested by Ming v1: - initial version https://lore.kernel.org/linux-block/20201126095152.19151-1-dwagner@suse.de/ block/blk-mq.c | 25 ------------------------- 1 file changed, 25 deletions(-)