syzbot

======================================================
[ INFO: possible circular locking dependency detected ]
4.4.163+ #122 Not tainted
-------------------------------------------------------
syz-executor742/12963 is trying to acquire lock:
 (&p->lock){+.+.+.}, at: [<ffffffff815014ed>] seq_read+0xdd/0x12b0 fs/seq_file.c:178

but task is already holding lock:
 (sb_writers#4){.+.+.+}, at: [<ffffffff81494bfa>] file_start_write include/linux/fs.h:2541 [inline]
 (sb_writers#4){.+.+.+}, at: [<ffffffff81494bfa>] do_sendfile+0x89a/0xb80 fs/read_write.c:1226

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

       [<ffffffff8120301e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff81498f1e>] percpu_down_read include/linux/percpu-rwsem.h:26 [inline]
       [<ffffffff81498f1e>] __sb_start_write+0x1ae/0x310 fs/super.c:1221
       [<ffffffff816bb237>] sb_start_write include/linux/fs.h:1515 [inline]
       [<ffffffff816bb237>] ext4_run_li_request fs/ext4/super.c:2674 [inline]
       [<ffffffff816bb237>] ext4_lazyinit_thread+0x1a7/0x750 fs/ext4/super.c:2773
       [<ffffffff811340d8>] kthread+0x268/0x300 kernel/kthread.c:211
       [<ffffffff827127c5>] ret_from_fork+0x55/0x80 arch/x86/entry/entry_64.S:510

       [<ffffffff8120301e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff82706e5b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff82706e5b>] mutex_lock_nested+0xbb/0x8d0 kernel/locking/mutex.c:621
       [<ffffffff816c5334>] ext4_register_li_request+0x304/0x7a0 fs/ext4/super.c:2961
       [<ffffffff816c6b38>] ext4_remount+0x1368/0x1bb0 fs/ext4/super.c:4911
       [<ffffffff8149c1c8>] do_remount_sb2+0x428/0x7d0 fs/super.c:771
       [<ffffffff814fc10e>] do_remount fs/namespace.c:2335 [inline]
       [<ffffffff814fc10e>] do_mount+0x101e/0x2a10 fs/namespace.c:2848
       [<ffffffff814fe651>] SYSC_mount fs/namespace.c:3051 [inline]
       [<ffffffff814fe651>] SyS_mount+0x191/0x1c0 fs/namespace.c:3029
       [<ffffffff827123e1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

       [<ffffffff8120301e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff82706e5b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff82706e5b>] mutex_lock_nested+0xbb/0x8d0 kernel/locking/mutex.c:621
       [<ffffffff816c50b7>] ext4_register_li_request+0x87/0x7a0 fs/ext4/super.c:2934
       [<ffffffff816c6b38>] ext4_remount+0x1368/0x1bb0 fs/ext4/super.c:4911
       [<ffffffff8149c1c8>] do_remount_sb2+0x428/0x7d0 fs/super.c:771
       [<ffffffff814fc10e>] do_remount fs/namespace.c:2335 [inline]
       [<ffffffff814fc10e>] do_mount+0x101e/0x2a10 fs/namespace.c:2848
       [<ffffffff814fe651>] SYSC_mount fs/namespace.c:3051 [inline]
       [<ffffffff814fe651>] SyS_mount+0x191/0x1c0 fs/namespace.c:3029
       [<ffffffff827123e1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

       [<ffffffff8120301e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff8270d3d2>] down_read+0x42/0x60 kernel/locking/rwsem.c:22
       [<ffffffff8149b8e1>] iterate_supers+0xe1/0x260 fs/super.c:537
       [<ffffffff819aa1b4>] selinux_complete_init+0x2f/0x31 security/selinux/hooks.c:6154
       [<ffffffff8199be06>] security_load_policy+0x886/0x9b0 security/selinux/ss/services.c:2060
       [<ffffffff81971d31>] sel_write_load+0x191/0xfc0 security/selinux/selinuxfs.c:535
       [<ffffffff81490e8c>] __vfs_write+0x11c/0x3e0 fs/read_write.c:489
       [<ffffffff81492b3e>] vfs_write+0x17e/0x4e0 fs/read_write.c:538
       [<ffffffff81495179>] SYSC_write fs/read_write.c:585 [inline]
       [<ffffffff81495179>] SyS_write+0xd9/0x1c0 fs/read_write.c:577
       [<ffffffff827123e1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

       [<ffffffff8120301e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff82706e5b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff82706e5b>] mutex_lock_nested+0xbb/0x8d0 kernel/locking/mutex.c:621
       [<ffffffff8196f817>] sel_commit_bools_write+0x87/0x250 security/selinux/selinuxfs.c:1142
       [<ffffffff81490e8c>] __vfs_write+0x11c/0x3e0 fs/read_write.c:489
       [<ffffffff8149125a>] __kernel_write+0x10a/0x350 fs/read_write.c:511
       [<ffffffff8152c2cd>] write_pipe_buf+0x15d/0x1f0 fs/splice.c:1074
       [<ffffffff8152d164>] splice_from_pipe_feed fs/splice.c:776 [inline]
       [<ffffffff8152d164>] __splice_from_pipe+0x364/0x790 fs/splice.c:901
       [<ffffffff81530229>] splice_from_pipe+0xf9/0x170 fs/splice.c:936
       [<ffffffff8153032c>] default_file_splice_write+0x3c/0x80 fs/splice.c:1086
       [<ffffffff815313f1>] do_splice_from fs/splice.c:1128 [inline]
       [<ffffffff815313f1>] do_splice fs/splice.c:1404 [inline]
       [<ffffffff815313f1>] SYSC_splice fs/splice.c:1707 [inline]
       [<ffffffff815313f1>] SyS_splice+0xde1/0x1430 fs/splice.c:1690
       [<ffffffff827123e1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

       [<ffffffff8120301e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff82706e5b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff82706e5b>] mutex_lock_nested+0xbb/0x8d0 kernel/locking/mutex.c:621
       [<ffffffff814acc7c>] __pipe_lock fs/pipe.c:86 [inline]
       [<ffffffff814acc7c>] fifo_open+0x15c/0x9e0 fs/pipe.c:896
       [<ffffffff8148bc7d>] do_dentry_open+0x38d/0xbd0 fs/open.c:749
       [<ffffffff8148f3ea>] vfs_open+0x12a/0x210 fs/open.c:862
       [<ffffffff814befcc>] do_last fs/namei.c:3222 [inline]
       [<ffffffff814befcc>] path_openat+0x50c/0x39a0 fs/namei.c:3359
       [<ffffffff814c60f7>] do_filp_open+0x197/0x270 fs/namei.c:3393
       [<ffffffff814a215f>] do_open_execat+0x10f/0x6f0 fs/exec.c:800
       [<ffffffff814a7711>] do_execveat_common.isra.14+0x6a1/0x1f00 fs/exec.c:1573
       [<ffffffff814a98e2>] do_execve fs/exec.c:1679 [inline]
       [<ffffffff814a98e2>] SYSC_execve fs/exec.c:1760 [inline]
       [<ffffffff814a98e2>] SyS_execve+0x42/0x50 fs/exec.c:1755
       [<ffffffff827126f5>] return_from_execve+0x0/0x23

       [<ffffffff8120301e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff8270800c>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff8270800c>] mutex_lock_killable_nested+0xcc/0xa10 kernel/locking/mutex.c:641
       [<ffffffff810cae41>] mm_access+0x51/0x140 kernel/fork.c:857
       [<ffffffff815e2109>] proc_pid_auxv+0x29/0xd0 fs/proc/base.c:409
       [<ffffffff815db26d>] proc_single_show+0xfd/0x170 fs/proc/base.c:805
       [<ffffffff81500a93>] traverse+0x363/0x920 fs/seq_file.c:124
       [<ffffffff81502115>] seq_read+0xd05/0x12b0 fs/seq_file.c:195
       [<ffffffff814915e8>] do_loop_readv_writev+0x148/0x1e0 fs/read_write.c:680
       [<ffffffff81493421>] do_readv_writev+0x581/0x6f0 fs/read_write.c:810
       [<ffffffff81493608>] vfs_readv+0x78/0xb0 fs/read_write.c:834
       [<ffffffff8152f7af>] kernel_readv fs/splice.c:586 [inline]
       [<ffffffff8152f7af>] default_file_splice_read+0x50f/0x8f0 fs/splice.c:662
       [<ffffffff8152b687>] do_splice_to+0xf7/0x140 fs/splice.c:1154
       [<ffffffff8152b912>] splice_direct_to_actor+0x242/0x830 fs/splice.c:1226
       [<ffffffff8152c0a3>] do_splice_direct+0x1a3/0x270 fs/splice.c:1337
       [<ffffffff81494844>] do_sendfile+0x4e4/0xb80 fs/read_write.c:1227
       [<ffffffff81496833>] SYSC_sendfile64 fs/read_write.c:1282 [inline]
       [<ffffffff81496833>] SyS_sendfile64+0xc3/0x150 fs/read_write.c:1274
       [<ffffffff827123e1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

       [<ffffffff811ff43c>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
       [<ffffffff811ff43c>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
       [<ffffffff811ff43c>] validate_chain kernel/locking/lockdep.c:2144 [inline]
       [<ffffffff811ff43c>] __lock_acquire+0x3e6c/0x5f10 kernel/locking/lockdep.c:3213
       [<ffffffff8120301e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff82706e5b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff82706e5b>] mutex_lock_nested+0xbb/0x8d0 kernel/locking/mutex.c:621
       [<ffffffff815014ed>] seq_read+0xdd/0x12b0 fs/seq_file.c:178
       [<ffffffff815d889d>] proc_reg_read+0xfd/0x180 fs/proc/inode.c:202
       [<ffffffff814915e8>] do_loop_readv_writev+0x148/0x1e0 fs/read_write.c:680
       [<ffffffff81493421>] do_readv_writev+0x581/0x6f0 fs/read_write.c:810
       [<ffffffff81493608>] vfs_readv+0x78/0xb0 fs/read_write.c:834
       [<ffffffff8152f7af>] kernel_readv fs/splice.c:586 [inline]
       [<ffffffff8152f7af>] default_file_splice_read+0x50f/0x8f0 fs/splice.c:662
       [<ffffffff8152b687>] do_splice_to+0xf7/0x140 fs/splice.c:1154
       [<ffffffff8152b912>] splice_direct_to_actor+0x242/0x830 fs/splice.c:1226
       [<ffffffff8152c0a3>] do_splice_direct+0x1a3/0x270 fs/splice.c:1337
       [<ffffffff81494844>] do_sendfile+0x4e4/0xb80 fs/read_write.c:1227
       [<ffffffff81496833>] SYSC_sendfile64 fs/read_write.c:1282 [inline]
       [<ffffffff81496833>] SyS_sendfile64+0xc3/0x150 fs/read_write.c:1274
       [<ffffffff827123e1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

other info that might help us debug this:

Chain exists of:
 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(sb_writers#4);
                               lock(&eli->li_list_mtx);
                               lock(sb_writers#4);
  lock(&p->lock);

 *** DEADLOCK ***

1 lock held by syz-executor742/12963:
 #0:  (sb_writers#4){.+.+.+}, at: [<ffffffff81494bfa>] file_start_write include/linux/fs.h:2541 [inline]
 #0:  (sb_writers#4){.+.+.+}, at: [<ffffffff81494bfa>] do_sendfile+0x89a/0xb80 fs/read_write.c:1226

stack backtrace:
CPU: 1 PID: 12963 Comm: syz-executor742 Not tainted 4.4.163+ #122
 0000000000000000 c3a07f746dcbb295 ffff8801d8a8ef78 ffffffff81aa556d
 ffffffff83ac0550 ffffffff83ab4190 ffffffff83aaffc0 ffff8801d96508e8
 ffff8801d9650000 ffff8801d8a8efc0 ffffffff813a8827 0000000000000001
Call Trace:
 [<ffffffff81aa556d>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81aa556d>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff813a8827>] print_circular_bug.cold.34+0x2f7/0x432 kernel/locking/lockdep.c:1226
 [<ffffffff811ff43c>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
 [<ffffffff811ff43c>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
 [<ffffffff811ff43c>] validate_chain kernel/locking/lockdep.c:2144 [inline]
 [<ffffffff811ff43c>] __lock_acquire+0x3e6c/0x5f10 kernel/locking/lockdep.c:3213
 [<ffffffff8120301e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
 [<ffffffff82706e5b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
 [<ffffffff82706e5b>] mutex_lock_nested+0xbb/0x8d0 kernel/locking/mutex.c:621
 [<ffffffff815014ed>] seq_read+0xdd/0x12b0 fs/seq_file.c:178
 [<ffffffff815d889d>] proc_reg_read+0xfd/0x180 fs/proc/inode.c:202
 [<ffffffff814915e8>] do_loop_readv_writev+0x148/0x1e0 fs/read_write.c:680
 [<ffffffff81493421>] do_readv_writev+0x581/0x6f0 fs/read_write.c:810
 [<ffffffff81493608>] vfs_readv+0x78/0xb0 fs/read_write.c:834
 [<ffffffff8152f7af>] kernel_readv fs/splice.c:586 [inline]
 [<ffffffff8152f7af>] default_file_splice_read+0x50f/0x8f0 fs/splice.c:662
 [<ffffffff8152b687>] do_splice_to+0xf7/0x140 fs/splice.c:1154
 [<ffffffff8152b912>] splice_direct_to_actor+0x242/0x830 fs/splice.c:1226
 [<ffffffff8152c0a3>] do_splice_direct+0x1a3/0x270 fs/splice.c:1337
 [<ffffffff81494844>] do_sendfile+0x4e4/0xb80 fs/read_write.c:1227
 [<ffffffff81496833>] SYSC_sendfile64 fs/read_write.c:1282 [inline]
 [<ffffffff81496833>] SyS_sendfile64+0xc3/0x150 fs/read_write.c:1274
 [<ffffffff827123e1>] entry_SYSCALL_64_fastpath+0x1e/0x9a