====================================================== WARNING: possible circular locking dependency detected 4.13.0-rc6+ #33 Not tainted ------------------------------------------------------ syz-executor1/21367 is trying to acquire lock: (sk_lock-AF_KCM){+.+.+.}, at: [] lock_sock include/net/sock.h:1459 [inline] (sk_lock-AF_KCM){+.+.+.}, at: [] kcm_sendpage+0x16e/0x1880 net/kcm/kcmsock.c:774 but task is already holding lock: (k-sk_lock-AF_KCM){+.+.+.}, at: [] lock_sock include/net/sock.h:1459 [inline] (k-sk_lock-AF_KCM){+.+.+.}, at: [] kcm_sendmsg+0x1ec/0x2200 net/kcm/kcmsock.c:910 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (k-sk_lock-AF_KCM){+.+.+.}: lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3855 lock_sock_nested+0xc2/0x110 net/core/sock.c:2762 lock_sock include/net/sock.h:1459 [inline] kcm_sendpage+0x16e/0x1880 net/kcm/kcmsock.c:774 kernel_sendpage+0x8d/0xe0 net/socket.c:3387 kcm_write_msgs+0x404/0x1b80 net/kcm/kcmsock.c:646 kcm_sendmsg+0x1446/0x2200 net/kcm/kcmsock.c:1035 sock_sendmsg_nosec net/socket.c:633 [inline] sock_sendmsg+0xca/0x110 net/socket.c:643 sock_write_iter+0x31a/0x5d0 net/socket.c:912 call_write_iter include/linux/fs.h:1743 [inline] new_sync_write fs/read_write.c:457 [inline] __vfs_write+0x684/0x970 fs/read_write.c:470 vfs_write+0x189/0x510 fs/read_write.c:518 SYSC_write fs/read_write.c:565 [inline] SyS_write+0xef/0x220 fs/read_write.c:557 entry_SYSCALL_64_fastpath+0x1f/0xbe -> #0 (sk_lock-AF_KCM){+.+.+.}: check_prev_add kernel/locking/lockdep.c:1844 [inline] check_prevs_add kernel/locking/lockdep.c:1954 [inline] validate_chain kernel/locking/lockdep.c:2281 [inline] __lock_acquire+0x2f2c/0x3dc0 kernel/locking/lockdep.c:3367 lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3855 lock_sock_nested+0xc2/0x110 net/core/sock.c:2762 lock_sock include/net/sock.h:1459 [inline] kcm_sendpage+0x16e/0x1880 net/kcm/kcmsock.c:774 kernel_sendpage+0x8d/0xe0 net/socket.c:3387 kcm_write_msgs+0x404/0x1b80 net/kcm/kcmsock.c:646 kcm_sendmsg+0x1446/0x2200 net/kcm/kcmsock.c:1035 sock_sendmsg_nosec net/socket.c:633 [inline] sock_sendmsg+0xca/0x110 net/socket.c:643 sock_write_iter+0x31a/0x5d0 net/socket.c:912 call_write_iter include/linux/fs.h:1743 [inline] new_sync_write fs/read_write.c:457 [inline] __vfs_write+0x684/0x970 fs/read_write.c:470 vfs_write+0x189/0x510 fs/read_write.c:518 SYSC_write fs/read_write.c:565 [inline] SyS_write+0xef/0x220 fs/read_write.c:557 entry_SYSCALL_64_fastpath+0x1f/0xbe other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(k-sk_lock-AF_KCM); lock(sk_lock-AF_KCM); lock(k-sk_lock-AF_KCM); lock(sk_lock-AF_KCM); *** DEADLOCK *** 1 lock held by syz-executor1/21367: #0: (k-sk_lock-AF_KCM){+.+.+.}, at: [] lock_sock include/net/sock.h:1459 [inline] #0: (k-sk_lock-AF_KCM){+.+.+.}, at: [] kcm_sendmsg+0x1ec/0x2200 net/kcm/kcmsock.c:910 stack backtrace: CPU: 0 PID: 21367 Comm: syz-executor1 Not tainted 4.13.0-rc6+ #33 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:16 [inline] dump_stack+0x194/0x257 lib/dump_stack.c:52 print_circular_bug+0x358/0x400 kernel/locking/lockdep.c:1218 check_prev_add kernel/locking/lockdep.c:1844 [inline] check_prevs_add kernel/locking/lockdep.c:1954 [inline] validate_chain kernel/locking/lockdep.c:2281 [inline] __lock_acquire+0x2f2c/0x3dc0 kernel/locking/lockdep.c:3367 lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3855 lock_sock_nested+0xc2/0x110 net/core/sock.c:2762 lock_sock include/net/sock.h:1459 [inline] kcm_sendpage+0x16e/0x1880 net/kcm/kcmsock.c:774 kernel_sendpage+0x8d/0xe0 net/socket.c:3387 kcm_write_msgs+0x404/0x1b80 net/kcm/kcmsock.c:646 kcm_sendmsg+0x1446/0x2200 net/kcm/kcmsock.c:1035 sock_sendmsg_nosec net/socket.c:633 [inline] sock_sendmsg+0xca/0x110 net/socket.c:643 sock_write_iter+0x31a/0x5d0 net/socket.c:912 call_write_iter include/linux/fs.h:1743 [inline] new_sync_write fs/read_write.c:457 [inline] __vfs_write+0x684/0x970 fs/read_write.c:470 vfs_write+0x189/0x510 fs/read_write.c:518 SYSC_write fs/read_write.c:565 [inline] SyS_write+0xef/0x220 fs/read_write.c:557 entry_SYSCALL_64_fastpath+0x1f/0xbe RIP: 0033:0x451e59 RSP: 002b:00007fb418948c08 EFLAGS: 00000216 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 0000000000718000 RCX: 0000000000451e59 RDX: 0000000000000046 RSI: 0000000020759fba RDI: 0000000000000018 RBP: 0000000000000086 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000216 R12: 00000000004bb465 R13: 00000000ffffffff R14: 0000000000000010 R15: 0000000000000003