[PATCH 3.16 313/357] blk-mq: Avoid race condition with uninitialized requests

[Greg Kroah-Hartman]

3.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Hildenbrand <dahi@xxxxxxxxxxxxxxxxxx>

commit 683d0e126232d898a481daa3a4ca032c2b1a9660 upstream.

This patch should fix the bug reported in
https://lkml.org/lkml/2014/9/11/249.

We have to initialize at least the atomic_flags and the cmd_flags when
allocating storage for the requests.

Otherwise blk_mq_timeout_check() might dereference uninitialized
pointers when racing with the creation of a request.

Also move the reset of cmd_flags for the initializing code to the point
where a request is freed. So we will never end up with pending flush
request indicators that might trigger dereferences of invalid pointers
in blk_mq_timeout_check().

Signed-off-by: David Hildenbrand <dahi@xxxxxxxxxxxxxxxxxx>
Reported-by: Paulo De Rezende Pinatti <ppinatti@xxxxxxxxxxxxxxxxxx>
Tested-by: Paulo De Rezende Pinatti <ppinatti@xxxxxxxxxxxxxxxxxx>
Acked-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 block/blk-mq.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -219,7 +219,6 @@ __blk_mq_alloc_request(struct blk_mq_all
 	if (tag != BLK_MQ_TAG_FAIL) {
 		rq = data->hctx->tags->rqs[tag];
 
-		rq->cmd_flags = 0;
 		if (blk_mq_tag_busy(data->hctx)) {
 			rq->cmd_flags = REQ_MQ_INFLIGHT;
 			atomic_inc(&data->hctx->nr_active);
@@ -274,6 +273,7 @@ static void __blk_mq_free_request(struct
 
 	if (rq->cmd_flags & REQ_MQ_INFLIGHT)
 		atomic_dec(&hctx->nr_active);
+	rq->cmd_flags = 0;
 
 	clear_bit(REQ_ATOM_STARTED, &rq->atomic_flags);
 	blk_mq_put_tag(hctx, tag, &ctx->last_tag);
@@ -1411,6 +1411,8 @@ static struct blk_mq_tags *blk_mq_init_r
 		left -= to_do * rq_size;
 		for (j = 0; j < to_do; j++) {
 			tags->rqs[i] = p;
+			tags->rqs[i]->atomic_flags = 0;
+			tags->rqs[i]->cmd_flags = 0;
 			if (set->ops->init_request) {
 				if (set->ops->init_request(set->driver_data,
 						tags->rqs[i], hctx_idx, i,


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