blk-mq-tag: check for NULL rq when iterating tags (7f5562d5) · Commits · 戴 / test

Since we introduced blk-mq-sched, the tags->rqs[] array has been dynamically assigned. So we need to check for NULL when iterating, since there's a window of time where the bit is set, but we haven't dynamically assigned the tags->rqs[] array position yet. This is perfectly safe, since the memory backing of the request is never going away while the device is alive. Reviewed-by:

Bart Van Assche <bart.vanassche@wdc.com> Reviewed-by:

Omar Sandoval <osandov@fb.com> Signed-off-by:

Jens Axboe <axboe@kernel.dk>

block/blk-mq-tag.c

+12 −2

Original line number	Diff line number	Diff line
		@@ -214,7 +214,11 @@ static bool bt_iter(struct sbitmap bitmap, unsigned int bitnr, void data)
		bitnr += tags->nr_reserved_tags;
		rq = tags->rqs[bitnr];

		if (rq->q == hctx->queue)
		/*
		* We can hit rq == NULL here, because the tagging functions
		* test and set the bit before assining ->rqs[].
		*/
		if (rq && rq->q == hctx->queue)
		iter_data->fn(hctx, rq, iter_data->data, reserved);
		return true;
		}
		@@ -248,9 +252,15 @@ static bool bt_tags_iter(struct sbitmap bitmap, unsigned int bitnr, void data)

		if (!reserved)
		bitnr += tags->nr_reserved_tags;
		rq = tags->rqs[bitnr];

		/*
		* We can hit rq == NULL here, because the tagging functions
		* test and set the bit before assining ->rqs[].
		*/
		rq = tags->rqs[bitnr];
		if (rq)
		iter_data->fn(rq, iter_data->data, reserved);

		return true;
		}

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