From 7f5562d5ecc44c757599b201df928ba52fa05047 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Fri, 4 Aug 2017 13:37:03 -0600 Subject: [PATCH] blk-mq-tag: check for NULL rq when iterating tags 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 Reviewed-by: Omar Sandoval Signed-off-by: Jens Axboe --- block/blk-mq-tag.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c index d0be72ccb091..dc9e6dac5a2a 100644 --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -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]; - iter_data->fn(rq, iter_data->data, reserved); + /* + * 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; }