====================================================== WARNING: possible circular locking dependency detected 5.0.0-rc4-next-20190201 #25 Not tainted ------------------------------------------------------ syz-executor2/18554 is trying to acquire lock: 000000006010e4f8 (&sig->cred_guard_mutex){+.+.}, at: do_io_accounting+0x1f4/0x830 fs/proc/base.c:2743 but task is already holding lock: 000000008987cd6b (&p->lock){+.+.}, at: seq_read+0x71/0x1130 fs/seq_file.c:161 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #3 (&p->lock){+.+.}: __mutex_lock_common kernel/locking/mutex.c:925 [inline] __mutex_lock+0xf7/0x1310 kernel/locking/mutex.c:1072 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087 seq_read+0x71/0x1130 fs/seq_file.c:161 proc_reg_read+0x1fe/0x2c0 fs/proc/inode.c:227 do_loop_readv_writev fs/read_write.c:700 [inline] do_loop_readv_writev fs/read_write.c:687 [inline] do_iter_read+0x4a9/0x660 fs/read_write.c:921 vfs_readv+0xf0/0x160 fs/read_write.c:983 kernel_readv fs/splice.c:362 [inline] default_file_splice_read+0x475/0x890 fs/splice.c:417 do_splice_to+0x12a/0x190 fs/splice.c:880 splice_direct_to_actor+0x2d2/0x970 fs/splice.c:957 do_splice_direct+0x1da/0x2a0 fs/splice.c:1066 do_sendfile+0x597/0xd00 fs/read_write.c:1436 __do_sys_sendfile64 fs/read_write.c:1497 [inline] __se_sys_sendfile64 fs/read_write.c:1483 [inline] __x64_sys_sendfile64+0x1dd/0x220 fs/read_write.c:1483 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe -> #2 (sb_writers#3){.+.+}: percpu_down_read_preempt_disable include/linux/percpu-rwsem.h:36 [inline] percpu_down_read include/linux/percpu-rwsem.h:59 [inline] __sb_start_write+0x20b/0x360 fs/super.c:1613 sb_start_write include/linux/fs.h:1607 [inline] mnt_want_write+0x3f/0xc0 fs/namespace.c:358 ovl_want_write+0x76/0xa0 fs/overlayfs/util.c:24 ovl_create_object+0xb3/0x2c0 fs/overlayfs/dir.c:599 ovl_create+0x28/0x30 fs/overlayfs/dir.c:630 lookup_open+0x12e0/0x1b10 fs/namei.c:3234 do_last fs/namei.c:3324 [inline] path_openat+0x14ac/0x46e0 fs/namei.c:3535 do_filp_open+0x1a1/0x280 fs/namei.c:3565 do_sys_open+0x3fe/0x5d0 fs/open.c:1063 ksys_open include/linux/syscalls.h:1365 [inline] __do_sys_creat fs/open.c:1121 [inline] __se_sys_creat fs/open.c:1119 [inline] __x64_sys_creat+0x61/0x80 fs/open.c:1119 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe -> #1 (&ovl_i_mutex_dir_key[depth]){++++}: down_read+0x3b/0x90 kernel/locking/rwsem.c:24 inode_lock_shared include/linux/fs.h:770 [inline] lookup_slow+0x4a/0x80 fs/namei.c:1687 walk_component+0x74b/0x2000 fs/namei.c:1810 link_path_walk.part.0+0x980/0x1340 fs/namei.c:2141 link_path_walk fs/namei.c:2072 [inline] path_openat+0x202/0x46e0 fs/namei.c:3534 do_filp_open+0x1a1/0x280 fs/namei.c:3565 do_open_execat+0x137/0x690 fs/exec.c:856 __do_execve_file.isra.0+0x178d/0x23f0 fs/exec.c:1758 do_execveat_common fs/exec.c:1865 [inline] do_execve fs/exec.c:1882 [inline] __do_sys_execve fs/exec.c:1963 [inline] __se_sys_execve fs/exec.c:1958 [inline] __x64_sys_execve+0x8f/0xc0 fs/exec.c:1958 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe -> #0 (&sig->cred_guard_mutex){+.+.}: lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:3826 __mutex_lock_common kernel/locking/mutex.c:925 [inline] __mutex_lock+0xf7/0x1310 kernel/locking/mutex.c:1072 mutex_lock_killable_nested+0x16/0x20 kernel/locking/mutex.c:1102 do_io_accounting+0x1f4/0x830 fs/proc/base.c:2743 proc_tgid_io_accounting+0x23/0x30 fs/proc/base.c:2792 proc_single_show+0xf6/0x180 fs/proc/base.c:743 seq_read+0x4db/0x1130 fs/seq_file.c:229 __vfs_read+0x116/0x8c0 fs/read_write.c:416 vfs_read+0x194/0x3e0 fs/read_write.c:452 ksys_pread64+0x183/0x1c0 fs/read_write.c:626 __do_sys_pread64 fs/read_write.c:636 [inline] __se_sys_pread64 fs/read_write.c:633 [inline] __x64_sys_pread64+0x97/0xf0 fs/read_write.c:633 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe other info that might help us debug this: Chain exists of: &sig->cred_guard_mutex --> sb_writers#3 --> &p->lock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&p->lock); lock(sb_writers#3); lock(&p->lock); lock(&sig->cred_guard_mutex); *** DEADLOCK *** 1 lock held by syz-executor2/18554: #0: 000000008987cd6b (&p->lock){+.+.}, at: seq_read+0x71/0x1130 fs/seq_file.c:161 stack backtrace: CPU: 1 PID: 18554 Comm: syz-executor2 Not tainted 5.0.0-rc4-next-20190201 #25 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x172/0x1f0 lib/dump_stack.c:113 print_circular_bug.isra.0.cold+0x1cc/0x28f kernel/locking/lockdep.c:1224 check_prev_add kernel/locking/lockdep.c:1855 [inline] check_prevs_add kernel/locking/lockdep.c:1968 [inline] validate_chain kernel/locking/lockdep.c:2339 [inline] __lock_acquire+0x2e7a/0x4790 kernel/locking/lockdep.c:3320 lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:3826 __mutex_lock_common kernel/locking/mutex.c:925 [inline] __mutex_lock+0xf7/0x1310 kernel/locking/mutex.c:1072 mutex_lock_killable_nested+0x16/0x20 kernel/locking/mutex.c:1102 do_io_accounting+0x1f4/0x830 fs/proc/base.c:2743 proc_tgid_io_accounting+0x23/0x30 fs/proc/base.c:2792 proc_single_show+0xf6/0x180 fs/proc/base.c:743 seq_read+0x4db/0x1130 fs/seq_file.c:229 __vfs_read+0x116/0x8c0 fs/read_write.c:416 vfs_read+0x194/0x3e0 fs/read_write.c:452 ksys_pread64+0x183/0x1c0 fs/read_write.c:626 __do_sys_pread64 fs/read_write.c:636 [inline] __se_sys_pread64 fs/read_write.c:633 [inline] __x64_sys_pread64+0x97/0xf0 fs/read_write.c:633 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x457e39 Code: ad b8 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 7b b8 fb ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007fd4d4125c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000011 RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 0000000000457e39 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000004 RBP: 000000000073bfa0 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007fd4d41266d4 R13: 00000000004c48d9 R14: 00000000004d8048 R15: 00000000ffffffff