From 8b428f42f3edfd62422aa7ad87049ab232a2eaa9 Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Wed, 9 Jul 2025 19:17:44 +0800 Subject: [PATCH] nbd: fix lockdep deadlock warning nbd grabs device lock nbd->config_lock for updating nr_hw_queues, this ways cause the following lock dependency: -> #2 (&disk->open_mutex){+.+.}-{4:4}: lock_acquire kernel/locking/lockdep.c:5871 [inline] lock_acquire+0x1ac/0x448 kernel/locking/lockdep.c:5828 __mutex_lock_common kernel/locking/mutex.c:602 [inline] __mutex_lock+0x166/0x1292 kernel/locking/mutex.c:747 mutex_lock_nested+0x14/0x1c kernel/locking/mutex.c:799 __del_gendisk+0x132/0xac6 block/genhd.c:706 del_gendisk+0xf6/0x19a block/genhd.c:819 nbd_dev_remove+0x3c/0xf2 drivers/block/nbd.c:268 nbd_dev_remove_work+0x1c/0x26 drivers/block/nbd.c:284 process_one_work+0x96a/0x1f32 kernel/workqueue.c:3238 process_scheduled_works kernel/workqueue.c:3321 [inline] worker_thread+0x5ce/0xde8 kernel/workqueue.c:3402 kthread+0x39c/0x7d4 kernel/kthread.c:464 ret_from_fork_kernel+0x2a/0xbb2 arch/riscv/kernel/process.c:214 ret_from_fork_kernel_asm+0x16/0x18 arch/riscv/kernel/entry.S:327 -> #1 (&set->update_nr_hwq_lock){++++}-{4:4}: lock_acquire kernel/locking/lockdep.c:5871 [inline] lock_acquire+0x1ac/0x448 kernel/locking/lockdep.c:5828 down_write+0x9c/0x19a kernel/locking/rwsem.c:1577 blk_mq_update_nr_hw_queues+0x3e/0xb86 block/blk-mq.c:5041 nbd_start_device+0x140/0xb2c drivers/block/nbd.c:1476 nbd_genl_connect+0xae0/0x1b24 drivers/block/nbd.c:2201 genl_family_rcv_msg_doit+0x206/0x2e6 net/netlink/genetlink.c:1115 genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline] genl_rcv_msg+0x514/0x78e net/netlink/genetlink.c:1210 netlink_rcv_skb+0x206/0x3be net/netlink/af_netlink.c:2534 genl_rcv+0x36/0x4c net/netlink/genetlink.c:1219 netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline] netlink_unicast+0x4f0/0x82c net/netlink/af_netlink.c:1339 netlink_sendmsg+0x85e/0xdd6 net/netlink/af_netlink.c:1883 sock_sendmsg_nosec net/socket.c:712 [inline] __sock_sendmsg+0xcc/0x160 net/socket.c:727 ____sys_sendmsg+0x63e/0x79c net/socket.c:2566 ___sys_sendmsg+0x144/0x1e6 net/socket.c:2620 __sys_sendmsg+0x188/0x246 net/socket.c:2652 __do_sys_sendmsg net/socket.c:2657 [inline] __se_sys_sendmsg net/socket.c:2655 [inline] __riscv_sys_sendmsg+0x70/0xa2 net/socket.c:2655 syscall_handler+0x94/0x118 arch/riscv/include/asm/syscall.h:112 do_trap_ecall_u+0x396/0x530 arch/riscv/kernel/traps.c:341 handle_exception+0x146/0x152 arch/riscv/kernel/entry.S:197 -> #0 (&nbd->config_lock){+.+.}-{4:4}: check_noncircular+0x132/0x146 kernel/locking/lockdep.c:2178 check_prev_add kernel/locking/lockdep.c:3168 [inline] check_prevs_add kernel/locking/lockdep.c:3287 [inline] validate_chain kernel/locking/lockdep.c:3911 [inline] __lock_acquire+0x12b2/0x24ea kernel/locking/lockdep.c:5240 lock_acquire kernel/locking/lockdep.c:5871 [inline] lock_acquire+0x1ac/0x448 kernel/locking/lockdep.c:5828 __mutex_lock_common kernel/locking/mutex.c:602 [inline] __mutex_lock+0x166/0x1292 kernel/locking/mutex.c:747 mutex_lock_nested+0x14/0x1c kernel/locking/mutex.c:799 refcount_dec_and_mutex_lock+0x60/0xd8 lib/refcount.c:118 nbd_config_put+0x3a/0x610 drivers/block/nbd.c:1423 nbd_release+0x94/0x15c drivers/block/nbd.c:1735 blkdev_put_whole+0xac/0xee block/bdev.c:721 bdev_release+0x3fe/0x600 block/bdev.c:1144 blkdev_release+0x1a/0x26 block/fops.c:684 __fput+0x382/0xa8c fs/file_table.c:465 ____fput+0x1c/0x26 fs/file_table.c:493 task_work_run+0x16a/0x25e kernel/task_work.c:227 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline] exit_to_user_mode_loop+0x118/0x134 kernel/entry/common.c:114 exit_to_user_mode_prepare include/linux/entry-common.h:330 [inline] syscall_exit_to_user_mode_work include/linux/entry-common.h:414 [inline] syscall_exit_to_user_mode include/linux/entry-common.h:449 [inline] do_trap_ecall_u+0x3f0/0x530 arch/riscv/kernel/traps.c:355 handle_exception+0x146/0x152 arch/riscv/kernel/entry.S:197 Also it isn't necessary to require nbd->config_lock, because blk_mq_update_nr_hw_queues() does grab tagset lock for sync everything. Fixes the issue by releasing ->config_lock & retry in case of concurrent updating nr_hw_queues. Fixes: 98e68f67020c ("block: prevent adding/deleting disk during updating nr_hw_queues") Reported-by: syzbot+2bcecf3c38cb3e8fdc8d@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/6855034f.a00a0220.137b3.0031.GAE@google.com Reviewed-by: Yu Kuai Cc: Nilay Shroff Signed-off-by: Ming Lei Reviewed-by: Nilay Shroff Link: https://lore.kernel.org/r/20250709111744.2353050-1-ming.lei@redhat.com Signed-off-by: Jens Axboe --- drivers/block/nbd.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index 7bdc7eb808ea9..709bad75c47b5 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -1473,7 +1473,17 @@ static int nbd_start_device(struct nbd_device *nbd) return -EINVAL; } - blk_mq_update_nr_hw_queues(&nbd->tag_set, config->num_connections); +retry: + mutex_unlock(&nbd->config_lock); + blk_mq_update_nr_hw_queues(&nbd->tag_set, num_connections); + mutex_lock(&nbd->config_lock); + + /* if another code path updated nr_hw_queues, retry until succeed */ + if (num_connections != config->num_connections) { + num_connections = config->num_connections; + goto retry; + } + nbd->pid = task_pid_nr(current); nbd_parse_flags(nbd); -- 2.47.2