On 18/4/11 07:02, Bart Van Assche wrote:
> 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 <[email protected]>
> Fixes: a063057d7c73 ("block: Fix a race between request queue removal and the
> block cgroup controller")
> Signed-off-by: Bart Van Assche <[email protected]>
> Cc: Ming Lei <[email protected]>
> Cc: Joseph Qi <[email protected]>
I've tested using the following steps:
1) start a fio job with buffered write;
2) then remove the scsi device that fio write to:
echo "scsi remove-single-device ${dev}" > /proc/scsi/scsi
After applying this patch, the reported oops has gone.
Tested-by: Joseph Qi <[email protected]>
> ---
>
> Changes compared to v2: converted two ternary expressions into if-statements.
>
> Changes compared to v1: guarded the blk_queue_exit() inside the loop with "if
> (q)".
>
> block/blk-core.c | 35 +++++++++++++++++++++++++++++------
> 1 file changed, 29 insertions(+), 6 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 34e2f2227fd9..39308e874ffa 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -2386,8 +2386,20 @@ blk_qc_t generic_make_request(struct bio *bio)
> * yet.
> */
> struct bio_list bio_list_on_stack[2];
> + blk_mq_req_flags_t flags = 0;
> + struct request_queue *q = bio->bi_disk->queue;
> blk_qc_t ret = BLK_QC_T_NONE;
>
> + if (bio->bi_opf & REQ_NOWAIT)
> + flags = BLK_MQ_REQ_NOWAIT;
> + 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 +2436,22 @@ 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 = 0;
> + if (bio->bi_opf & REQ_NOWAIT)
> + flags = BLK_MQ_REQ_NOWAIT;
> + 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 +2459,6 @@ 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 +2485,8 @@ 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);
>
