Re: [PATCH V2 2/3] block: don't drain in-progress dispatch in blk_cleanup_queue()

Bart Van Assche
2019-04-01T15:15:04Z

On Mon, 2019-04-01 at 12:42 +0800, Ming Lei wrote:
> Now freeing hw queue resource is moved to hctx's release handler,
> we don't need to worry about the race between blk_cleanup_queue and
> run queue any more.
>
> So don't drain in-progress dispatch in blk_cleanup_queue().
>
> This is basically revert of c2856ae2f315 ("blk-mq: quiesce queue before
> freeing queue").
>
> Cc: Dongli Zhang <dongli.zhang@oracle.com>
> Cc: James Smart <james.smart@broadcom.com>
> Cc: Bart Van Assche <bart.vanassche@wdc.com>
> Cc: linux-scsi@vger.kernel.org,
> Cc: Martin K . Petersen <martin.petersen@oracle.com>,
> Cc: Christoph Hellwig <hch@lst.de>,
> Cc: James E . J . Bottomley <jejb@linux.vnet.ibm.com>,
> Cc: jianchao wang <jianchao.w.wang@oracle.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
> block/blk-core.c | 12 ------------
> 1 file changed, 12 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index b3bbf8a5110d..491dc0295778 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -347,18 +347,6 @@ void blk_cleanup_queue(struct request_queue *q)
>
> blk_queue_flag_set(QUEUE_FLAG_DEAD, q);
>
> - /*
> - * make sure all in-progress dispatch are completed because
> - * blk_freeze_queue() can only complete all requests, and
> - * dispatch may still be in-progress since we dispatch requests
> - * from more than one contexts.
> - *
> - * We rely on driver to deal with the race in case that queue
> - * initialization isn't done.
> - */
> - if (queue_is_mq(q) && blk_queue_init_done(q))
> - blk_mq_quiesce_queue(q);
> -
> /* for synchronous bio-based driver finish in-flight integrity i/o */
> blk_flush_integrity();

Many block drivers clean up resources immediately after blk_cleanup_queue()
returns. Not waiting for ongoing .queue_rq() calls to finish is wrong because
it can cause block drivers to destroy resources that are in use by a concurrent
.queue_rq() call.

Bart.