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 <[email protected]>
Cc: Hannes Reinecke <[email protected]>
Cc: James Smart <[email protected]>
Cc: Ming Lei <[email protected]>
Cc: Jianchao Wang <[email protected]>
Cc: Dongli Zhang <[email protected]>
Cc: <[email protected]>
Fixes: a063057d7c73 ("block: Fix a race between request queue removal and the
block cgroup controller") # v4.17.
Reported-by: James Smart <[email protected]>
Signed-off-by: Bart Van Assche <[email protected]>
---
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;
queue_for_each_hw_ctx(q, hctx, i) {
if (blk_mq_hctx_stopped(hctx))
continue;
blk_mq_run_hw_queue(hctx, async);
}
+ percpu_ref_put(&q->q_usage_counter);
}
EXPORT_SYMBOL(blk_mq_run_hw_queues);
--
2.21.0.196.g041f5ea1cf98
