| Message ID | 1475033064-31848-1-git-send-email-krisman@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 09/27/2016 09:24 PM, Gabriel Krisman Bertazi wrote: > Commit 0e87e58bf60e ("blk-mq: improve warning for running a queue on the > wrong CPU") attempts to avoid triggering the WARN_ON in > __blk_mq_run_hw_queue when the expected CPU is dead. Problem is, in the > last batch execution before round robin, blk_mq_hctx_next_cpu can > schedule a dead CPU and also update next_cpu to the next alive CPU in > the mask, which will trigger the WARN_ON despite the previous > workaround. > > The following patch fixes this scenario by always scheduling the value > in hctx->next_cpu. This changes the moment when we round-robin the CPU > running the hctx, but it really doesn't matter, since it still executes > BLK_MQ_CPU_WORK_BATCH times in a row before switching to another CPU. Thanks, this looks good. Applied for 4.9.
diff --git a/block/blk-mq.c b/block/blk-mq.c index 0be5577b0d56..367d21215345 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -883,7 +883,7 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx) return WORK_CPU_UNBOUND; if (--hctx->next_cpu_batch <= 0) { - int cpu = hctx->next_cpu, next_cpu; + int next_cpu; next_cpu = cpumask_next(hctx->next_cpu, hctx->cpumask); if (next_cpu >= nr_cpu_ids) @@ -891,8 +891,6 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx) hctx->next_cpu = next_cpu; hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH; - - return cpu; } return hctx->next_cpu;
Commit 0e87e58bf60e ("blk-mq: improve warning for running a queue on the wrong CPU") attempts to avoid triggering the WARN_ON in __blk_mq_run_hw_queue when the expected CPU is dead. Problem is, in the last batch execution before round robin, blk_mq_hctx_next_cpu can schedule a dead CPU and also update next_cpu to the next alive CPU in the mask, which will trigger the WARN_ON despite the previous workaround. The following patch fixes this scenario by always scheduling the value in hctx->next_cpu. This changes the moment when we round-robin the CPU running the hctx, but it really doesn't matter, since it still executes BLK_MQ_CPU_WORK_BATCH times in a row before switching to another CPU. Fixes: 0e87e58bf60e ("blk-mq: improve warning for running a queue on the wrong CPU") Signed-off-by: Gabriel Krisman Bertazi <krisman@linux.vnet.ibm.com> --- block/blk-mq.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)