Commit 4b422cb9 authored by Junxiao Bi's avatar Junxiao Bi Committed by Konrad Rzeszutek Wilk

xen-blkfront: fix mq start/stop race

When ring buf full, hw queue will be stopped. While blkif interrupt consume
request and make free space in ring buf, hw queue will be started again.
But since start queue is protected by spin lock while stop not, that will
cause a race.

interrupt:                                      process:
blkif_interrupt()                               blkif_queue_rq()
 kick_pending_request_queues_locked()
   blk_mq_start_stopped_hw_queues()
      clear_bit(BLK_MQ_S_STOPPED, &hctx->state)
	                                             blk_mq_stop_hw_queue(hctx)
	  blk_mq_run_hw_queue(hctx, async)

If ring buf is made empty in this case, interrupt will never come, then the
hw queue will be stopped forever, all processes waiting for the pending io
in the queue will hung.
Signed-off-by: default avatarJunxiao Bi <junxiao.bi@oracle.com>
Reviewed-by: default avatarAnkur Arora <ankur.a.arora@oracle.com>
Acked-by: default avatarRoger Pau Monné <roger.pau@citrix.com>
Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent 76451d79
...@@ -906,8 +906,8 @@ static blk_status_t blkif_queue_rq(struct blk_mq_hw_ctx *hctx, ...@@ -906,8 +906,8 @@ static blk_status_t blkif_queue_rq(struct blk_mq_hw_ctx *hctx,
return BLK_STS_IOERR; return BLK_STS_IOERR;
out_busy: out_busy:
spin_unlock_irqrestore(&rinfo->ring_lock, flags);
blk_mq_stop_hw_queue(hctx); blk_mq_stop_hw_queue(hctx);
spin_unlock_irqrestore(&rinfo->ring_lock, flags);
return BLK_STS_RESOURCE; return BLK_STS_RESOURCE;
} }
......
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