From: Ming Lei ming.lei@redhat.com
commit a9ed27a764156929efe714033edb3e9023c5f321 upstream.
is_flush_rq() is called from bt_iter()/bt_tags_iter(), and runs the following check:
hctx->fq->flush_rq == req
but the passed hctx from bt_iter()/bt_tags_iter() may be NULL because:
1) memory re-order in blk_mq_rq_ctx_init():
rq->mq_hctx = data->hctx; ... refcount_set(&rq->ref, 1);
OR
2) tag re-use and ->rqs[] isn't updated with new request.
Fix the issue by re-writing is_flush_rq() as:
return rq->end_io == flush_end_io;
which turns out simpler to follow and immune to data race since we have ordered WRITE rq->end_io and refcount_set(&rq->ref, 1).
Fixes: 2e315dc07df0 ("blk-mq: grab rq->refcount before calling ->fn in blk_mq_tagset_busy_iter") Cc: "Blank-Burian, Markus, Dr." blankburian@uni-muenster.de Cc: Yufen Yu yuyufen@huawei.com Signed-off-by: Ming Lei ming.lei@redhat.com Link: https://lore.kernel.org/r/20210818010925.607383-1-ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk Cc: Yi Zhang yi.zhang@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- block/blk-flush.c | 5 +++++ block/blk-mq.c | 2 +- block/blk.h | 6 +----- 3 files changed, 7 insertions(+), 6 deletions(-)
--- a/block/blk-flush.c +++ b/block/blk-flush.c @@ -263,6 +263,11 @@ static void flush_end_io(struct request spin_unlock_irqrestore(&fq->mq_flush_lock, flags); }
+bool is_flush_rq(struct request *rq) +{ + return rq->end_io == flush_end_io; +} + /** * blk_kick_flush - consider issuing flush request * @q: request_queue being kicked --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -929,7 +929,7 @@ static bool blk_mq_req_expired(struct re
void blk_mq_put_rq_ref(struct request *rq) { - if (is_flush_rq(rq, rq->mq_hctx)) + if (is_flush_rq(rq)) rq->end_io(rq, 0); else if (refcount_dec_and_test(&rq->ref)) __blk_mq_free_request(rq); --- a/block/blk.h +++ b/block/blk.h @@ -44,11 +44,7 @@ static inline void __blk_get_queue(struc kobject_get(&q->kobj); }
-static inline bool -is_flush_rq(struct request *req, struct blk_mq_hw_ctx *hctx) -{ - return hctx->fq->flush_rq == req; -} +bool is_flush_rq(struct request *req);
struct blk_flush_queue *blk_alloc_flush_queue(int node, int cmd_size, gfp_t flags);