summaryrefslogtreecommitdiffstats
path: root/block/blk-map.c
diff options
context:
space:
mode:
authorChengming Zhou <zhouchengming@bytedance.com>2023-09-01 14:03:06 +0200
committerJens Axboe <axboe@kernel.dk>2023-09-01 16:18:25 +0200
commit5a26e45edb4690d58406178b5a9ea4c6dcf2c105 (patch)
treef98bcf289507ce1b44190ac04070ed7ecf703ad9 /block/blk-map.c
parents390/dasd: fix string length handling (diff)
downloadlinux-5a26e45edb4690d58406178b5a9ea4c6dcf2c105.tar.xz
linux-5a26e45edb4690d58406178b5a9ea4c6dcf2c105.zip
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 'block/blk-map.c')
0 files changed, 0 insertions, 0 deletions