blk-mq: fix kernel oops in blk_mq_tag_idle()

HW queues may be unmapped in some cases, such as blk_mq_update_nr_hw_queues(), then we need to check it before calling blk_mq_tag_idle(), otherwise the following kernel oops can be triggered, so fix it by checking if the hw queue is unmapped since it doesn't make sense to idle the tags any more after hw queues are unmapped.

[  440.771298] Workqueue: nvme-wq nvme_rdma_del_ctrl_work [nvme_rdma]
[  440.779104] task: ffff894bae755ee0 ti: ffff893bf9bc8000 task.ti: ffff893bf9bc8000
[  440.788359] RIP: 0010:[<ffffffffb730e2b4>]  [<ffffffffb730e2b4>] __blk_mq_tag_idle+0x24/0x40
[  440.798697] RSP: 0018:ffff893bf9bcbd10  EFLAGS: 00010286
[  440.805538] RAX: 0000000000000000 RBX: ffff895bb131dc00 RCX: 000000000000011f
[  440.814426] RDX: 00000000ffffffff RSI: 0000000000000120 RDI: ffff895bb131dc00
[  440.823301] RBP: ffff893bf9bcbd10 R08: 000000000001b860 R09: 4a51d361c00c0000
[  440.832193] R10: b5907f32b4cc7003 R11: ffffd6cabfb57000 R12: ffff894bafd1e008
[  440.841091] R13: 0000000000000001 R14: ffff895baf770000 R15: 0000000000000080
[  440.849988] FS:  0000000000000000(0000) GS:ffff894bbdcc0000(0000) knlGS:0000000000000000
[  440.859955] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  440.867274] CR2: 0000000000000008 CR3: 000000103d098000 CR4: 00000000001407e0
[  440.876169] Call Trace:
[  440.879818]  [<ffffffffb7309d68>] blk_mq_exit_hctx+0xd8/0xe0
[  440.887051]  [<ffffffffb730dc40>] blk_mq_free_queue+0xf0/0x160
[  440.894465]  [<ffffffffb72ff679>] blk_cleanup_queue+0xd9/0x150
[  440.901881]  [<ffffffffc08a802b>] nvme_ns_remove+0x5b/0xb0 [nvme_core]
[  440.910068]  [<ffffffffc08a811b>] nvme_remove_namespaces+0x3b/0x60 [nvme_core]
[  440.919026]  [<ffffffffc08b817b>] __nvme_rdma_remove_ctrl+0x2b/0xb0 [nvme_rdma]
[  440.928079]  [<ffffffffc08b8237>] nvme_rdma_del_ctrl_work+0x17/0x20 [nvme_rdma]
[  440.937126]  [<ffffffffb70ab58a>] process_one_work+0x17a/0x440
[  440.944517]  [<ffffffffb70ac3a8>] worker_thread+0x278/0x3c0
[  440.951607]  [<ffffffffb70ac130>] ? manage_workers.isra.24+0x2a0/0x2a0
[  440.959760]  [<ffffffffb70b352f>] kthread+0xcf/0xe0
[  440.966055]  [<ffffffffb70b3460>] ? insert_kthread_work+0x40/0x40
[  440.973715]  [<ffffffffb76d8658>] ret_from_fork+0x58/0x90
[  440.980586]  [<ffffffffb70b3460>] ? insert_kthread_work+0x40/0x40
[  440.988229] Code: 5b 41 5c 5d c3 66 90 0f 1f 44 00 00 48 8b 87 20 01 00 00 f0 0f ba 77 40 01 19 d2 85 d2 75 08 c3 0f 1f 80 00 00 00 00 55 48 89 e5 <f0> ff 48 08 48 8d 78 10 e8 7f 0f 05 00 5d c3 0f 1f 00 66 2e 0f
[  441.011620] RIP  [<ffffffffb730e2b4>] __blk_mq_tag_idle+0x24/0x40
[  441.019301]  RSP <ffff893bf9bcbd10>
[  441.024052] CR2: 0000000000000008

---
 block/blk-mq.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

index 111e1aa5562f..e258ad8dc171 100644
@@ -2015,7 +2015,8 @@ static void blk_mq_exit_hctx(struct request_queue *q,
 {
 	blk_mq_debugfs_unregister_hctx(hctx);
 
-	blk_mq_tag_idle(hctx);
+	if (blk_mq_hw_queue_mapped(hctx))
+		blk_mq_tag_idle(hctx);
 
 	if (set->ops->exit_request)
 		set->ops->exit_request(set, hctx->fq->flush_rq, hctx_idx);

2.9.5

Seems cleaner to just move the mapped check to the idling function, especially since we already have the same check in the other spot where we call the idling.

index 61deab0b5a5a..10e7e1ef8297 100644
@@ -63,6 +63,8 @@ static inline bool blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
 
 static inline void blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
 {
+	if (!blk_mq_hw_queue_mapped(hctx))
+		return;
 	if (!(hctx->flags & BLK_MQ_F_TAG_SHARED))
 		return;
 

index 111e1aa5562f..4d9f79bfdca2 100644
@@ -873,11 +873,8 @@ static void blk_mq_timeout_work(struct work_struct *work)
 	} else {
 		struct blk_mq_hw_ctx *hctx;
 
-		queue_for_each_hw_ctx(q, hctx, i) {
-			/* the hctx may be unmapped, so check it here */
-			if (blk_mq_hw_queue_mapped(hctx))
-				blk_mq_tag_idle(hctx);
-		}
+		queue_for_each_hw_ctx(q, hctx, i)
+			blk_mq_tag_idle(hctx);
 	}
 	blk_queue_exit(q);
 }

Jens Axboe

Ho hum, I guess that requires shuffling some code/includes to actually do that. I'll just apply yours as-is.

Jens Axboe

Yes, that need to move blk_mq_hw_queue_mapped() into blk-mq-tag.h since the two headers are included by each other, seem some cleanup are needed for headers.

Thanks,
Ming