Because blkcg_exit_queue() is now called from inside blk_cleanup_queue()
it is no longer safe to access cgroup information during or after the
blk_cleanup_queue() call. Hence protect the generic_make_request_checks()
call with blk_queue_enter() / blk_queue_exit().

Reported-by: Ming Lei <ming....@redhat.com>
Fixes: a063057d7c73 ("block: Fix a race between request queue removal and the 
block cgroup controller")
Signed-off-by: Bart Van Assche <bart.vanass...@wdc.com>
Cc: Ming Lei <ming....@redhat.com>
Cc: Joseph Qi <joseph...@linux.alibaba.com>
---

Changes compared to v1: changed the blk_queue_exit() inside the loop with "if 
(q)".

 block/blk-core.c | 33 +++++++++++++++++++++++++++------
 1 file changed, 27 insertions(+), 6 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 34e2f2227fd9..181b1a688a5b 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2386,8 +2386,19 @@ blk_qc_t generic_make_request(struct bio *bio)
         * yet.
         */
        struct bio_list bio_list_on_stack[2];
+       blk_mq_req_flags_t flags = bio->bi_opf & REQ_NOWAIT ?
+               BLK_MQ_REQ_NOWAIT : 0;
+       struct request_queue *q = bio->bi_disk->queue;
        blk_qc_t ret = BLK_QC_T_NONE;
 
+       if (blk_queue_enter(q, flags) < 0) {
+               if (!blk_queue_dying(q) && (bio->bi_opf & REQ_NOWAIT))
+                       bio_wouldblock_error(bio);
+               else
+                       bio_io_error(bio);
+               return ret;
+       }
+
        if (!generic_make_request_checks(bio))
                goto out;
 
@@ -2424,11 +2435,21 @@ blk_qc_t generic_make_request(struct bio *bio)
        bio_list_init(&bio_list_on_stack[0]);
        current->bio_list = bio_list_on_stack;
        do {
-               struct request_queue *q = bio->bi_disk->queue;
-               blk_mq_req_flags_t flags = bio->bi_opf & REQ_NOWAIT ?
-                       BLK_MQ_REQ_NOWAIT : 0;
+               bool enter_succeeded = true;
+
+               if (unlikely(q != bio->bi_disk->queue)) {
+                       if (q)
+                               blk_queue_exit(q);
+                       q = bio->bi_disk->queue;
+                       flags = bio->bi_opf & REQ_NOWAIT ? BLK_MQ_REQ_NOWAIT :
+                               0;
+                       if (blk_queue_enter(q, flags) < 0) {
+                               enter_succeeded = false;
+                               q = NULL;
+                       }
+               }
 
-               if (likely(blk_queue_enter(q, flags) == 0)) {
+               if (enter_succeeded) {
                        struct bio_list lower, same;
 
                        /* Create a fresh bio_list for all subordinate requests 
*/
@@ -2436,8 +2457,6 @@ blk_qc_t generic_make_request(struct bio *bio)
                        bio_list_init(&bio_list_on_stack[0]);
                        ret = q->make_request_fn(q, bio);
 
-                       blk_queue_exit(q);
-
                        /* sort new bios into those for a lower level
                         * and those for the same level
                         */
@@ -2464,6 +2483,8 @@ blk_qc_t generic_make_request(struct bio *bio)
        current->bio_list = NULL; /* deactivate */
 
 out:
+       if (q)
+               blk_queue_exit(q);
        return ret;
 }
 EXPORT_SYMBOL(generic_make_request);
-- 
2.16.2

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