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authorChengming Zhou <zhouchengming@bytedance.com>2023-09-01 20:03:06 +0800
committerJens Axboe <axboe@kernel.dk>2023-09-01 08:18:25 -0600
commit5a26e45edb4690d58406178b5a9ea4c6dcf2c105 (patch)
treef98bcf289507ce1b44190ac04070ed7ecf703ad9 /drivers/block
parentf7cf22424665043787a96a66a048ff6b2cfd473c (diff)
null_blk: fix poll request timeout handling
When doing io_uring benchmark on /dev/nullb0, it's easy to crash the kernel if poll requests timeout triggered, as reported by David. [1] BUG: kernel NULL pointer dereference, address: 0000000000000008 Workqueue: kblockd blk_mq_timeout_work RIP: 0010:null_timeout_rq+0x4e/0x91 Call Trace: ? null_timeout_rq+0x4e/0x91 blk_mq_handle_expired+0x31/0x4b bt_iter+0x68/0x84 ? bt_tags_iter+0x81/0x81 __sbitmap_for_each_set.constprop.0+0xb0/0xf2 ? __blk_mq_complete_request_remote+0xf/0xf bt_for_each+0x46/0x64 ? __blk_mq_complete_request_remote+0xf/0xf ? percpu_ref_get_many+0xc/0x2a blk_mq_queue_tag_busy_iter+0x14d/0x18e blk_mq_timeout_work+0x95/0x127 process_one_work+0x185/0x263 worker_thread+0x1b5/0x227 This is indeed a race problem between null_timeout_rq() and null_poll(). null_poll() null_timeout_rq() spin_lock(&nq->poll_lock) list_splice_init(&nq->poll_list, &list) spin_unlock(&nq->poll_lock) while (!list_empty(&list)) req = list_first_entry() list_del_init() ... blk_mq_add_to_batch() // req->rq_next = NULL spin_lock(&nq->poll_lock) // rq->queuelist->next == NULL list_del_init(&rq->queuelist) spin_unlock(&nq->poll_lock) Fix these problems by setting requests state to MQ_RQ_COMPLETE under nq->poll_lock protection, in which null_timeout_rq() can safely detect this race and early return. Note this patch just fix the kernel panic when request timeout happen. [1] https://lore.kernel.org/all/3893581.1691785261@warthog.procyon.org.uk/ Fixes: 0a593fbbc245 ("null_blk: poll queue support") Reported-by: David Howells <dhowells@redhat.com> Tested-by: David Howells <dhowells@redhat.com> Reviewed-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> Link: https://lore.kernel.org/r/20230901120306.170520-2-chengming.zhou@linux.dev Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'drivers/block')
-rw-r--r--drivers/block/null_blk/main.c12
1 files changed, 10 insertions, 2 deletions
diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index 864013019d6b..968090935eb2 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -1643,9 +1643,12 @@ static int null_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob)
struct nullb_queue *nq = hctx->driver_data;
LIST_HEAD(list);
int nr = 0;
+ struct request *rq;
spin_lock(&nq->poll_lock);
list_splice_init(&nq->poll_list, &list);
+ list_for_each_entry(rq, &list, queuelist)
+ blk_mq_set_request_complete(rq);
spin_unlock(&nq->poll_lock);
while (!list_empty(&list)) {
@@ -1671,16 +1674,21 @@ static enum blk_eh_timer_return null_timeout_rq(struct request *rq)
struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
struct nullb_cmd *cmd = blk_mq_rq_to_pdu(rq);
- pr_info("rq %p timed out\n", rq);
-
if (hctx->type == HCTX_TYPE_POLL) {
struct nullb_queue *nq = hctx->driver_data;
spin_lock(&nq->poll_lock);
+ /* The request may have completed meanwhile. */
+ if (blk_mq_request_completed(rq)) {
+ spin_unlock(&nq->poll_lock);
+ return BLK_EH_DONE;
+ }
list_del_init(&rq->queuelist);
spin_unlock(&nq->poll_lock);
}
+ pr_info("rq %p timed out\n", rq);
+
/*
* If the device is marked as blocking (i.e. memory backed or zoned
* device), the submission path may be blocked waiting for resources