| From c02ebfdddbafa9a6a0f52fbd715e6bfa229af9d3 Mon Sep 17 00:00:00 2001 |
| From: Gabriel Krisman Bertazi <krisman@linux.vnet.ibm.com> |
| Date: Wed, 28 Sep 2016 00:24:24 -0300 |
| Subject: blk-mq: Always schedule hctx->next_cpu |
| |
| From: Gabriel Krisman Bertazi <krisman@linux.vnet.ibm.com> |
| |
| commit c02ebfdddbafa9a6a0f52fbd715e6bfa229af9d3 upstream. |
| |
| 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> |
| Signed-off-by: Jens Axboe <axboe@fb.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| block/blk-mq.c | 4 +--- |
| 1 file changed, 1 insertion(+), 3 deletions(-) |
| |
| --- a/block/blk-mq.c |
| +++ b/block/blk-mq.c |
| @@ -842,7 +842,7 @@ static int blk_mq_hctx_next_cpu(struct b |
| 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) |
| @@ -850,8 +850,6 @@ static int blk_mq_hctx_next_cpu(struct b |
| |
| hctx->next_cpu = next_cpu; |
| hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH; |
| - |
| - return cpu; |
| } |
| |
| return hctx->next_cpu; |