bisecting fixing commit since 3af409ca278d4a8d50e91f9f7c4c33b175645cf3 building syzkaller on 3e5ed8b45e7a561d6344a4d3d7bf3bfb8f24a7b3 testing commit 3af409ca278d4a8d50e91f9f7c4c33b175645cf3 with gcc (GCC) 10.2.1 20210217 kernel signature: 20c455d8a58ab564b3d2acb25c1b998aa7a1929f4ff4fed292c78b6985cb6102 run #0: crashed: WARNING: refcount bug in nbd_config_put run #1: crashed: WARNING: refcount bug in nbd_config_put run #2: crashed: KASAN: use-after-free Read in nbd_genl_connect run #3: crashed: KASAN: use-after-free Read in nbd_genl_connect run #4: crashed: KASAN: use-after-free Read in nbd_genl_connect run #5: crashed: KASAN: use-after-free Read in nbd_genl_connect run #6: crashed: KASAN: use-after-free Read in nbd_genl_connect run #7: crashed: WARNING: refcount bug in nbd_config_put run #8: crashed: KASAN: use-after-free Read in nbd_genl_connect run #9: crashed: KASAN: use-after-free Read in nbd_genl_connect run #10: crashed: WARNING: refcount bug in nbd_config_put run #11: crashed: KASAN: use-after-free Write in nbd_config_put run #12: crashed: WARNING: refcount bug in nbd_config_put run #13: crashed: KASAN: use-after-free Read in nbd_genl_connect run #14: crashed: KASAN: use-after-free Read in nbd_genl_connect run #15: crashed: KASAN: use-after-free Read in nbd_genl_connect run #16: crashed: KASAN: use-after-free Read in nbd_genl_connect run #17: crashed: KASAN: use-after-free Read in nbd_genl_connect run #18: crashed: KASAN: use-after-free Read in nbd_genl_connect run #19: crashed: KASAN: use-after-free Read in nbd_genl_connect testing current HEAD 13c62f5371e3eb4fc3400cfa26e64ca75f888008 testing commit 13c62f5371e3eb4fc3400cfa26e64ca75f888008 with gcc (GCC) 10.2.1 20210217 kernel signature: 764a1bd19f89a8cbd959d5ecfa5db18ed66ed905168192db6a0fe27c21b0e7fa all runs: crashed: possible deadlock in del_gendisk revisions tested: 2, total time: 21m50.242172947s (build: 14m10.90986583s, test: 6m54.645541633s) the crash still happens on HEAD commit msg: net/sched: act_ct: handle DNAT tuple collision crash: possible deadlock in del_gendisk netlink: 4 bytes leftover after parsing attributes in process `syz-executor.1'. ====================================================== WARNING: possible circular locking dependency detected 5.13.0-rc3-syzkaller #0 Not tainted ------------------------------------------------------ syz-executor.1/10167 is trying to acquire lock: ffff888142ce00a0 (&bdev->bd_mutex){+.+.}-{3:3}, at: del_gendisk+0x220/0x950 block/genhd.c:610 but task is already holding lock: ffffffff8b3f3c88 (nbd_index_mutex){+.+.}-{3:3}, at: refcount_dec_and_mutex_lock lib/refcount.c:118 [inline] ffffffff8b3f3c88 (nbd_index_mutex){+.+.}-{3:3}, at: refcount_dec_and_mutex_lock+0x2b/0xd0 lib/refcount.c:113 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (nbd_index_mutex){+.+.}-{3:3}: __mutex_lock_common kernel/locking/mutex.c:959 [inline] __mutex_lock+0x139/0x10c0 kernel/locking/mutex.c:1104 nbd_open+0x6f/0x630 drivers/block/nbd.c:1460 __blkdev_get+0x143/0x8f0 fs/block_dev.c:1311 blkdev_get_by_dev fs/block_dev.c:1451 [inline] blkdev_get_by_dev+0x1a7/0x5c0 fs/block_dev.c:1423 blkdev_open+0xf6/0x220 fs/block_dev.c:1546 do_dentry_open+0x42a/0xfb0 fs/open.c:826 do_open fs/namei.c:3361 [inline] path_openat+0x9ee/0x22b0 fs/namei.c:3494 do_filp_open+0x17f/0x3a0 fs/namei.c:3521 do_sys_openat2+0x11e/0x360 fs/open.c:1187 do_sys_open fs/open.c:1203 [inline] __do_sys_open fs/open.c:1211 [inline] __se_sys_open fs/open.c:1207 [inline] __x64_sys_open+0xfd/0x1a0 fs/open.c:1207 do_syscall_64+0x3a/0xb0 arch/x86/entry/common.c:47 entry_SYSCALL_64_after_hwframe+0x44/0xae -> #0 (&bdev->bd_mutex){+.+.}-{3:3}: check_prev_add kernel/locking/lockdep.c:2938 [inline] check_prevs_add kernel/locking/lockdep.c:3061 [inline] validate_chain kernel/locking/lockdep.c:3676 [inline] __lock_acquire+0x2a01/0x5560 kernel/locking/lockdep.c:4902 lock_acquire kernel/locking/lockdep.c:5512 [inline] lock_acquire+0x1ab/0x730 kernel/locking/lockdep.c:5477 __mutex_lock_common kernel/locking/mutex.c:959 [inline] __mutex_lock+0x139/0x10c0 kernel/locking/mutex.c:1104 del_gendisk+0x220/0x950 block/genhd.c:610 nbd_dev_remove drivers/block/nbd.c:226 [inline] nbd_put.part.0+0xa4/0x1b0 drivers/block/nbd.c:250 nbd_put drivers/block/nbd.c:1928 [inline] nbd_genl_connect+0xeee/0x1290 drivers/block/nbd.c:1968 genl_family_rcv_msg_doit+0x1e4/0x2f0 net/netlink/genetlink.c:739 genl_family_rcv_msg net/netlink/genetlink.c:783 [inline] genl_rcv_msg+0x27a/0x4a0 net/netlink/genetlink.c:800 netlink_rcv_skb+0x118/0x370 net/netlink/af_netlink.c:2504 genl_rcv+0x1f/0x30 net/netlink/genetlink.c:811 netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline] netlink_unicast+0x42e/0x700 net/netlink/af_netlink.c:1340 netlink_sendmsg+0x70e/0xbe0 net/netlink/af_netlink.c:1929 sock_sendmsg_nosec net/socket.c:654 [inline] sock_sendmsg+0xab/0xe0 net/socket.c:674 ____sys_sendmsg+0x5bf/0x7a0 net/socket.c:2350 ___sys_sendmsg+0xd3/0x150 net/socket.c:2404 __sys_sendmsg+0xb2/0x140 net/socket.c:2433 do_syscall_64+0x3a/0xb0 arch/x86/entry/common.c:47 entry_SYSCALL_64_after_hwframe+0x44/0xae other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(nbd_index_mutex); lock(&bdev->bd_mutex); lock(nbd_index_mutex); lock(&bdev->bd_mutex); *** DEADLOCK *** 3 locks held by syz-executor.1/10167: #0: ffffffff8c05aef0 (cb_lock){++++}-{3:3}, at: genl_rcv+0x10/0x30 net/netlink/genetlink.c:810 #1: ffffffff8c05afa8 (genl_mutex){+.+.}-{3:3}, at: genl_lock net/netlink/genetlink.c:33 [inline] #1: ffffffff8c05afa8 (genl_mutex){+.+.}-{3:3}, at: genl_rcv_msg+0x315/0x4a0 net/netlink/genetlink.c:798 #2: ffffffff8b3f3c88 (nbd_index_mutex){+.+.}-{3:3}, at: refcount_dec_and_mutex_lock lib/refcount.c:118 [inline] #2: ffffffff8b3f3c88 (nbd_index_mutex){+.+.}-{3:3}, at: refcount_dec_and_mutex_lock+0x2b/0xd0 lib/refcount.c:113 stack backtrace: CPU: 1 PID: 10167 Comm: syz-executor.1 Not tainted 5.13.0-rc3-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:79 [inline] dump_stack+0x93/0xc2 lib/dump_stack.c:120 check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2129 check_prev_add kernel/locking/lockdep.c:2938 [inline] check_prevs_add kernel/locking/lockdep.c:3061 [inline] validate_chain kernel/locking/lockdep.c:3676 [inline] __lock_acquire+0x2a01/0x5560 kernel/locking/lockdep.c:4902 lock_acquire kernel/locking/lockdep.c:5512 [inline] lock_acquire+0x1ab/0x730 kernel/locking/lockdep.c:5477 __mutex_lock_common kernel/locking/mutex.c:959 [inline] __mutex_lock+0x139/0x10c0 kernel/locking/mutex.c:1104 del_gendisk+0x220/0x950 block/genhd.c:610 nbd_dev_remove drivers/block/nbd.c:226 [inline] nbd_put.part.0+0xa4/0x1b0 drivers/block/nbd.c:250 nbd_put drivers/block/nbd.c:1928 [inline] nbd_genl_connect+0xeee/0x1290 drivers/block/nbd.c:1968 genl_family_rcv_msg_doit+0x1e4/0x2f0 net/netlink/genetlink.c:739 genl_family_rcv_msg net/netlink/genetlink.c:783 [inline] genl_rcv_msg+0x27a/0x4a0 net/netlink/genetlink.c:800 netlink_rcv_skb+0x118/0x370 net/netlink/af_netlink.c:2504 genl_rcv+0x1f/0x30 net/netlink/genetlink.c:811 netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline] netlink_unicast+0x42e/0x700 net/netlink/af_netlink.c:1340 netlink_sendmsg+0x70e/0xbe0 net/netlink/af_netlink.c:1929 sock_sendmsg_nosec net/socket.c:654 [inline] sock_sendmsg+0xab/0xe0 net/socket.c:674 ____sys_sendmsg+0x5bf/0x7a0 net/socket.c:2350 ___sys_sendmsg+0xd3/0x150 net/socket.c:2404 __sys_sendmsg+0xb2/0x140 net/socket.c:2433 do_syscall_64+0x3a/0xb0 arch/x86/entry/common.c:47 entry_SYSCALL_64_after_hwframe+0x44/0xae RIP: 0033:0x466019 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fc8a4fed188 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 000000000056bf60 RCX: 0000000000466019 RDX: 0000000002000800 RSI: 0000000020002580 RDI: 0000000000000004 RBP: 00000000004bd067 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056bf60 R13: 00007fff7a28d2ef R14: 00007fc8a4fed300 R15: 0000000000022000