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Subjectpossible deadlock in seq_read (2)
From
Hello,

syzbot found the following crash on:

HEAD commit: bcb67f0f Add linux-next specific files for 20190412
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=135b5e9f200000
kernel config: https://syzkaller.appspot.com/x/.config?x=35c479ecf64ba753
dashboard link: https://syzkaller.appspot.com/bug?extid=5378878b09e052edef7f
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+5378878b09e052edef7f@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
5.1.0-rc4-next-20190412 #24 Not tainted
------------------------------------------------------
syz-executor.5/30036 is trying to acquire lock:
00000000dfc2e8ba (&p->lock){+.+.}, at: seq_read+0x71/0x1130
fs/seq_file.c:161

but task is already holding lock:
00000000471a7795 (sb_writers#5){.+.+}, at: file_start_write
include/linux/fs.h:2825 [inline]
00000000471a7795 (sb_writers#5){.+.+}, at: do_sendfile+0x9b9/0xd00
fs/read_write.c:1442

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (sb_writers#5){.+.+}:
lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4211
percpu_down_read include/linux/percpu-rwsem.h:36 [inline]
__sb_start_write+0x20b/0x360 fs/super.c:1613
sb_start_write include/linux/fs.h:1621 [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:3232
do_last fs/namei.c:3322 [inline]
path_openat+0x14ac/0x46e0 fs/namei.c:3533
do_filp_open+0x1a1/0x280 fs/namei.c:3563
do_sys_open+0x3fe/0x5d0 fs/open.c:1069
ksys_open include/linux/syscalls.h:1373 [inline]
__do_sys_creat fs/open.c:1127 [inline]
__se_sys_creat fs/open.c:1125 [inline]
__x64_sys_creat+0x61/0x80 fs/open.c:1125
do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #2 (&ovl_i_mutex_dir_key[depth]){++++}:
lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4211
down_read+0x3b/0x90 kernel/locking/rwsem.c:24
inode_lock_shared include/linux/fs.h:782 [inline]
do_last fs/namei.c:3321 [inline]
path_openat+0x1e98/0x46e0 fs/namei.c:3533
do_filp_open+0x1a1/0x280 fs/namei.c:3563
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:1958 [inline]
__se_sys_execve fs/exec.c:1953 [inline]
__x64_sys_execve+0x8f/0xc0 fs/exec.c:1953
do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #1 (&sig->cred_guard_mutex){+.+.}:
lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4211
__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
lock_trace+0x4a/0xe0 fs/proc/base.c:388
proc_pid_syscall+0x8a/0x220 fs/proc/base.c:623
proc_single_show+0xf6/0x170 fs/proc/base.c:744
seq_read+0x4db/0x1130 fs/seq_file.c:229
do_loop_readv_writev fs/read_write.c:701 [inline]
do_loop_readv_writev fs/read_write.c:688 [inline]
do_iter_read+0x4a9/0x660 fs/read_write.c:922
vfs_readv+0xf0/0x160 fs/read_write.c:984
kernel_readv fs/splice.c:358 [inline]
default_file_splice_read+0x475/0x890 fs/splice.c:413
do_splice_to+0x12a/0x190 fs/splice.c:876
splice_direct_to_actor+0x2d2/0x970 fs/splice.c:953
do_splice_direct+0x1da/0x2a0 fs/splice.c:1062
do_sendfile+0x597/0xd00 fs/read_write.c:1443
__do_sys_sendfile64 fs/read_write.c:1504 [inline]
__se_sys_sendfile64 fs/read_write.c:1490 [inline]
__x64_sys_sendfile64+0x1dd/0x220 fs/read_write.c:1490
do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (&p->lock){+.+.}:
check_prevs_add kernel/locking/lockdep.c:2333 [inline]
validate_chain kernel/locking/lockdep.c:2714 [inline]
__lock_acquire+0x239c/0x3fb0 kernel/locking/lockdep.c:3701
lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4211
__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:701 [inline]
do_loop_readv_writev fs/read_write.c:688 [inline]
do_iter_read+0x4a9/0x660 fs/read_write.c:922
vfs_readv+0xf0/0x160 fs/read_write.c:984
kernel_readv fs/splice.c:358 [inline]
default_file_splice_read+0x475/0x890 fs/splice.c:413
do_splice_to+0x12a/0x190 fs/splice.c:876
splice_direct_to_actor+0x2d2/0x970 fs/splice.c:953
do_splice_direct+0x1da/0x2a0 fs/splice.c:1062
do_sendfile+0x597/0xd00 fs/read_write.c:1443
__do_sys_sendfile64 fs/read_write.c:1504 [inline]
__se_sys_sendfile64 fs/read_write.c:1490 [inline]
__x64_sys_sendfile64+0x1dd/0x220 fs/read_write.c:1490
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:
&p->lock --> &ovl_i_mutex_dir_key[depth] --> sb_writers#5

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(sb_writers#5);
lock(&ovl_i_mutex_dir_key[depth]);
lock(sb_writers#5);
lock(&p->lock);

*** DEADLOCK ***

1 lock held by syz-executor.5/30036:
#0: 00000000471a7795 (sb_writers#5){.+.+}, at: file_start_write
include/linux/fs.h:2825 [inline]
#0: 00000000471a7795 (sb_writers#5){.+.+}, at: do_sendfile+0x9b9/0xd00
fs/read_write.c:1442

stack backtrace:
CPU: 1 PID: 30036 Comm: syz-executor.5 Not tainted 5.1.0-rc4-next-20190412
#24
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:1571
check_prev_add.constprop.0+0xf11/0x23c0 kernel/locking/lockdep.c:2220
check_prevs_add kernel/locking/lockdep.c:2333 [inline]
validate_chain kernel/locking/lockdep.c:2714 [inline]
__lock_acquire+0x239c/0x3fb0 kernel/locking/lockdep.c:3701
lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4211
__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:701 [inline]
do_loop_readv_writev fs/read_write.c:688 [inline]
do_iter_read+0x4a9/0x660 fs/read_write.c:922
vfs_readv+0xf0/0x160 fs/read_write.c:984
kernel_readv fs/splice.c:358 [inline]
default_file_splice_read+0x475/0x890 fs/splice.c:413
do_splice_to+0x12a/0x190 fs/splice.c:876
splice_direct_to_actor+0x2d2/0x970 fs/splice.c:953
do_splice_direct+0x1da/0x2a0 fs/splice.c:1062
do_sendfile+0x597/0xd00 fs/read_write.c:1443
__do_sys_sendfile64 fs/read_write.c:1504 [inline]
__se_sys_sendfile64 fs/read_write.c:1490 [inline]
__x64_sys_sendfile64+0x1dd/0x220 fs/read_write.c:1490
do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x458c29
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:00007f0f57706c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 0000000000458c29
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000006
RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000020 R11: 0000000000000246 R12: 00007f0f577076d4
R13: 00000000004c5e10 R14: 00000000004da5c8 R15: 00000000ffffffff


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

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