syzkaller has found reproducer for the following crash on 4131d5166185d0d75b5f1d4bf362a9e0bac05598 git://git.cmpxchg.org/linux-mmots.git/master compiler: gcc (GCC) 7.1.1 20170620 .config is attached Raw console output is attached. syzkaller reproducer is attached. See https://goo.gl/kgGztJ for information about syzkaller reproducers binder: 3116:3117 transaction failed 29189/-22, size 0-0 line 2832 ====================================================== WARNING: possible circular locking dependency detected 4.15.0-rc1-mm1+ #29 Not tainted ------------------------------------------------------ syz-executor0/3121 is trying to acquire lock: (&p->lock){+.+.}, at: [<00000000a7751419>] seq_read+0xd5/0x13d0 fs/seq_file.c:165 but task is already holding lock: (sb_writers){.+.+}, at: [<00000000048429cb>] file_start_write include/linux/fs.h:2715 [inline] (sb_writers){.+.+}, at: [<00000000048429cb>] do_sendfile+0xaec/0xe90 fs/read_write.c:1412 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #3 (sb_writers){.+.+}: spin_lock include/linux/spinlock.h:315 [inline] devtmpfsd+0x224/0x4b0 drivers/base/devtmpfs.c:392 -> #2 ((completion)&req.done){+.+.}: lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4004 complete_acquire include/linux/completion.h:40 [inline] __wait_for_common kernel/sched/completion.c:109 [inline] wait_for_common kernel/sched/completion.c:123 [inline] wait_for_completion+0xcb/0x7b0 kernel/sched/completion.c:144 devtmpfs_create_node+0x32b/0x4a0 drivers/base/devtmpfs.c:115 device_add+0x120f/0x1640 drivers/base/core.c:1824 device_create_groups_vargs+0x1f3/0x250 drivers/base/core.c:2430 device_create_vargs drivers/base/core.c:2470 [inline] device_create+0xda/0x110 drivers/base/core.c:2506 vcs_make_sysfs+0x35/0x60 drivers/tty/vt/vc_screen.c:629 vc_allocate+0x4b7/0x6b0 drivers/tty/vt/vt.c:797 con_install+0x52/0x440 drivers/tty/vt/vt.c:2876 tty_driver_install_tty drivers/tty/tty_io.c:1215 [inline] tty_init_dev+0xf6/0x4a0 drivers/tty/tty_io.c:1315 tty_open_by_driver drivers/tty/tty_io.c:1942 [inline] tty_open+0x608/0xab0 drivers/tty/tty_io.c:1990 chrdev_open+0x257/0x730 fs/char_dev.c:417 do_dentry_open+0x682/0xd70 fs/open.c:752 vfs_open+0x107/0x230 fs/open.c:866 do_last fs/namei.c:3379 [inline] path_openat+0x1157/0x3530 fs/namei.c:3519 do_filp_open+0x25b/0x3b0 fs/namei.c:3554 do_sys_open+0x502/0x6d0 fs/open.c:1059 SYSC_open fs/open.c:1077 [inline] SyS_open+0x2d/0x40 fs/open.c:1072 entry_SYSCALL_64_fastpath+0x1f/0x96 -> #1 (console_lock){+.+.}: lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4004 console_lock+0x4b/0x80 kernel/printk/printk.c:2047 c_start+0x18/0xf0 arch/x86/kernel/cpu/proc.c:146 seq_read+0x2f3/0x13d0 fs/seq_file.c:229 proc_reg_read+0xef/0x170 fs/proc/inode.c:217 __vfs_read+0xef/0xa00 fs/read_write.c:411 vfs_read+0x124/0x360 fs/read_write.c:447 SYSC_read fs/read_write.c:573 [inline] SyS_read+0xef/0x220 fs/read_write.c:566 entry_SYSCALL_64_fastpath+0x1f/0x96 -> #0 (&p->lock){+.+.}: check_prevs_add kernel/locking/lockdep.c:2031 [inline] validate_chain kernel/locking/lockdep.c:2473 [inline] __lock_acquire+0x3498/0x47f0 kernel/locking/lockdep.c:3500 lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4004 __mutex_lock_common kernel/locking/mutex.c:756 [inline] __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908 seq_read+0xd5/0x13d0 fs/seq_file.c:165 proc_reg_read+0xef/0x170 fs/proc/inode.c:217 do_loop_readv_writev fs/read_write.c:673 [inline] do_iter_read+0x3db/0x5b0 fs/read_write.c:897 vfs_readv+0x121/0x1c0 fs/read_write.c:959 kernel_readv fs/splice.c:361 [inline] default_file_splice_read+0x508/0xae0 fs/splice.c:416 do_splice_to+0x110/0x170 fs/splice.c:880 splice_direct_to_actor+0x242/0x820 fs/splice.c:952 do_splice_direct+0x2a7/0x3d0 fs/splice.c:1061 do_sendfile+0x5d5/0xe90 fs/read_write.c:1413 SYSC_sendfile64 fs/read_write.c:1468 [inline] SyS_sendfile64+0xbd/0x160 fs/read_write.c:1460 entry_SYSCALL_64_fastpath+0x1f/0x96 other info that might help us debug this: Chain exists of: &p->lock --> (completion)&req.done --> sb_writers Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(sb_writers); lock((completion)&req.done); lock(sb_writers); lock(&p->lock); *** DEADLOCK *** 1 lock held by syz-executor0/3121: #0: (sb_writers){.+.+}, at: [<00000000048429cb>] file_start_write include/linux/fs.h:2715 [inline] #0: (sb_writers){.+.+}, at: [<00000000048429cb>] do_sendfile+0xaec/0xe90 fs/read_write.c:1412 stack backtrace: CPU: 0 PID: 3121 Comm: syz-executor0 Not tainted 4.15.0-rc1-mm1+ #29 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:17 [inline] dump_stack+0x194/0x257 lib/dump_stack.c:53 print_circular_bug+0x42d/0x610 kernel/locking/lockdep.c:1271 check_prev_add+0x666/0x15f0 kernel/locking/lockdep.c:1914 check_prevs_add kernel/locking/lockdep.c:2031 [inline] validate_chain kernel/locking/lockdep.c:2473 [inline] __lock_acquire+0x3498/0x47f0 kernel/locking/lockdep.c:3500 lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4004 __mutex_lock_common kernel/locking/mutex.c:756 [inline] __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908 seq_read+0xd5/0x13d0 fs/seq_file.c:165 proc_reg_read+0xef/0x170 fs/proc/inode.c:217 do_loop_readv_writev fs/read_write.c:673 [inline] do_iter_read+0x3db/0x5b0 fs/read_write.c:897 vfs_readv+0x121/0x1c0 fs/read_write.c:959 kernel_readv fs/splice.c:361 [inline] default_file_splice_read+0x508/0xae0 fs/splice.c:416 do_splice_to+0x110/0x170 fs/splice.c:880 splice_direct_to_actor+0x242/0x820 fs/splice.c:952 do_splice_direct+0x2a7/0x3d0 fs/splice.c:1061 do_sendfile+0x5d5/0xe90 fs/read_write.c:1413 SYSC_sendfile64 fs/read_write.c:1468 [inline] SyS_sendfile64+0xbd/0x160 fs/read_write.c:1460 entry_SYSCALL_64_fastpath+0x1f/0x96 RIP: 0033:0x4529d9 RSP: 002b:00007fce2efc6c58 EFLAGS: 00000212 ORIG_RAX: 0000000000000028 RAX: ffffffffffffffda RBX: 00000000007580d8 RCX: 00000000004529d9 RDX: 00000000203e1000 RSI: 000000000000000e RDI: 000000000000000d RBP: 000000000000044a R08: 0000000000000000 R09: 0000000000000000 R10: 00000000000003fe R11: 0000000000000212 R12: 00000000006f3790