On Mon, 2018-04-09 at 14:54 +0800, Joseph Qi wrote:
> The oops happens during generic_make_request_checks(), in
> blk_throtl_bio() exactly.
> So if we want to bypass dying queue, we have to check this before
> generic_make_request_checks(), I think.

How about something like the patch below?

Thanks,

Bart.

Subject: [PATCH] blk-mq: Avoid that submitting a bio concurrently with device
 removal triggers a crash

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 a blk_queue_enter() / blk_queue_exit() pair.

---
 block/blk-core.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index d69888ff52f0..0c48bef8490f 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2388,9 +2388,24 @@ 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;
+       bool check_result;
        blk_qc_t ret = BLK_QC_T_NONE;
 
-       if (!generic_make_request_checks(bio))
+       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;
+       }
+
+       check_result = generic_make_request_checks(bio);
+       blk_queue_exit(q);
+
+       if (!check_result)
                goto out;
 
        /*
-- 
2.16.2

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