On Mon, Apr 01, 2019 at 02:20:12PM -0700, Bart Van Assche wrote:
Any request queue data structure may change while a queue is frozen. Hence make sure that blk_mq_run_hw_queues() does not access any hw queue while a request queue is frozen.
After blk_cleanup_queue() has marked a queue as dead it is no longer safe to access the hardware queue data structures. This patch avoids that blk_mq_run_hw_queues() crashes when called during or after blk_cleanup_queue() has freed the hardware queues. This patch is a variant of a patch posted by Hannes Reinecke ("[PATCH] block: don't call blk_mq_run_hw_queues() for dead or dying queues "). This patch is similar in nature to commit c246e80d8673 ("block: Avoid that request_fn is invoked on a dead queue"; v3.8). An example of a crash that is fixed by this patch:
BUG: unable to handle kernel NULL pointer dereference at (null) IP: [<ffffffff8135a10b>] sbitmap_any_bit_set+0xb/0x30 Call Trace: [<ffffffff81303a88>] blk_mq_run_hw_queues+0x48/0x90 [<ffffffff813053cc>] blk_mq_requeue_work+0x10c/0x120 [<ffffffff81098cb4>] process_one_work+0x154/0x410 [<ffffffff81099896>] worker_thread+0x116/0x4a0 [<ffffffff8109edb9>] kthread+0xc9/0xe0 [<ffffffff81619b05>] ret_from_fork+0x55/0x80
Cc: Christoph Hellwig hch@infradead.org Cc: Hannes Reinecke hare@suse.com Cc: James Smart james.smart@broadcom.com Cc: Ming Lei ming.lei@redhat.com Cc: Jianchao Wang jianchao.w.wang@oracle.com Cc: Dongli Zhang dongli.zhang@oracle.com Cc: stable@vger.kernel.org Fixes: a063057d7c73 ("block: Fix a race between request queue removal and the block cgroup controller") # v4.17. Reported-by: James Smart james.smart@broadcom.com Signed-off-by: Bart Van Assche bvanassche@acm.org
block/blk-mq.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/block/blk-mq.c b/block/blk-mq.c index 3ff3d7b49969..652d0c6d5945 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1499,12 +1499,20 @@ void blk_mq_run_hw_queues(struct request_queue *q, bool async) struct blk_mq_hw_ctx *hctx; int i;
- /*
* Do not run any hardware queues if the queue is frozen or if a* concurrent blk_cleanup_queue() call is removing any data* structures used by this function.*/- if (!percpu_ref_tryget(&q->q_usage_counter))
return;blk_mq_run_hw_queue(hctx, async); }
- percpu_ref_put(&q->q_usage_counter);
} EXPORT_SYMBOL(blk_mq_run_hw_queues);
I don't see it is necessary to add percpu_ref_tryget()/percpu_ref_put() in the fast path if we simply release all hctx resource in hctx's release handler by the following patch:
https://lore.kernel.org/linux-block/20190401044247.29881-2-ming.lei@redhat.c...
Even we can kill the percpu_ref_tryget_live()/percpu_ref_put() in scsi_end_request().
Thanks, Ming