From: Jens Axboe <axboe@kernel.dk>
Date: Mon, 1 Nov 2021 12:56:09 +0000 (-0600)
Subject: block: assign correct tag before doing prefetch of request
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=a22c00be90de188d36f4772ef7b268aa48d7010d;p=linux.git

block: assign correct tag before doing prefetch of request

Ensure that current tag is correctly assigned before attempting
to prefetch the first cacheline of the request.

Fixes: 92aff191cc5b ("block: prefetch request to be initialized")
Reported-and-tested-by: syzbot+cd20829ac44b92bf6ed0@syzkaller.appspotmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 221d1b7d10d66..4787d5b74aa3c 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -405,8 +405,8 @@ __blk_mq_alloc_requests_batch(struct blk_mq_alloc_data *data,
 	for (i = 0; tag_mask; i++) {
 		if (!(tag_mask & (1UL << i)))
 			continue;
-		prefetch(tags->static_rqs[tag]);
 		tag = tag_offset + i;
+		prefetch(tags->static_rqs[tag]);
 		tag_mask &= ~(1UL << i);
 		rq = blk_mq_rq_ctx_init(data, tags, tag, alloc_time_ns);
 		rq_list_add(data->cached_rq, rq);