Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 4.9 111/120] blk-mq: Always schedule hctx->next_cpu | Date | Wed, 18 Jan 2017 11:47:09 +0100 |
| |
4.9-stable review patch. If anyone has any objections, please let me know.
------------------
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 @@ -895,7 +895,7 @@ 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) @@ -903,8 +903,6 @@ 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;
| |