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Subjectpossible deadlock in mnt_want_write
From
Hello,

syzbot found the following crash on:

HEAD commit: 45ae4df92207 Merge tag 'armsoc-fixes' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10e7eee0400000
kernel config: https://syzkaller.appspot.com/x/.config?x=c0bdc4175608181c
dashboard link: https://syzkaller.appspot.com/bug?extid=ae82084b07d0297e566b
compiler: gcc (GCC) 8.0.1 20180413 (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+ae82084b07d0297e566b@syzkaller.appspotmail.com

device bridge_slave_0 left promiscuous mode
bridge0: port 1(bridge_slave_0) entered disabled state
IPVS: set_ctl: invalid protocol: 255 0.0.0.0:20004

======================================================
WARNING: possible circular locking dependency detected
4.18.0-rc5+ #159 Not tainted
------------------------------------------------------
syz-executor7/24660 is trying to acquire lock:
000000007bd46ec8 (sb_writers#15){.+.+}, at: sb_start_write
include/linux/fs.h:1554 [inline]
000000007bd46ec8 (sb_writers#15){.+.+}, at: mnt_want_write+0x3f/0xc0
fs/namespace.c:386

but task is already holding lock:
00000000a4a13f7a (&fi->mutex){+.+.}, at: fuse_lock_inode+0xaf/0xe0
fs/fuse/inode.c:363

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&fi->mutex){+.+.}:
__mutex_lock_common kernel/locking/mutex.c:757 [inline]
__mutex_lock+0x176/0x1820 kernel/locking/mutex.c:894
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:909
fuse_lock_inode+0xaf/0xe0 fs/fuse/inode.c:363
fuse_lookup+0x8f/0x4c0 fs/fuse/dir.c:359
__lookup_hash+0x12e/0x190 fs/namei.c:1505
filename_create+0x1e5/0x5b0 fs/namei.c:3646
user_path_create fs/namei.c:3703 [inline]
do_mkdirat+0xda/0x310 fs/namei.c:3842
__do_sys_mkdirat fs/namei.c:3861 [inline]
__se_sys_mkdirat fs/namei.c:3859 [inline]
__x64_sys_mkdirat+0x76/0xb0 fs/namei.c:3859
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #1 (&type->i_mutex_dir_key#5/1){+.+.}:
down_write_nested+0x93/0x130 kernel/locking/rwsem.c:192
inode_lock_nested include/linux/fs.h:750 [inline]
filename_create+0x1b2/0x5b0 fs/namei.c:3645
user_path_create fs/namei.c:3703 [inline]
do_mkdirat+0xda/0x310 fs/namei.c:3842
__do_sys_mkdirat fs/namei.c:3861 [inline]
__se_sys_mkdirat fs/namei.c:3859 [inline]
__x64_sys_mkdirat+0x76/0xb0 fs/namei.c:3859
nla_parse: 14 callbacks suppressed
netlink: 3 bytes leftover after parsing attributes in process
`syz-executor1'.
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (sb_writers#15){.+.+}:
lock_acquire+0x1e4/0x540 kernel/locking/lockdep.c:3924
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+0x1e9/0x300 fs/super.c:1403
sb_start_write include/linux/fs.h:1554 [inline]
mnt_want_write+0x3f/0xc0 fs/namespace.c:386
path_removexattr+0xf0/0x210 fs/xattr.c:703
__do_sys_removexattr fs/xattr.c:719 [inline]
__se_sys_removexattr fs/xattr.c:716 [inline]
__x64_sys_removexattr+0x59/0x80 fs/xattr.c:716
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

other info that might help us debug this:

Chain exists of:
sb_writers#15 --> &type->i_mutex_dir_key#5/1 --> &fi->mutex

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&fi->mutex);
lock(&type->i_mutex_dir_key#5/1);
lock(&fi->mutex);
lock(sb_writers#15);

*** DEADLOCK ***

1 lock held by syz-executor7/24660:
#0: 00000000a4a13f7a (&fi->mutex){+.+.}, at: fuse_lock_inode+0xaf/0xe0
fs/fuse/inode.c:363

stack backtrace:
CPU: 1 PID: 24660 Comm: syz-executor7 Not tainted 4.18.0-rc5+ #159
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+0x1c9/0x2b4 lib/dump_stack.c:113
print_circular_bug.isra.36.cold.57+0x1bd/0x27d
kernel/locking/lockdep.c:1227
check_prev_add kernel/locking/lockdep.c:1867 [inline]
check_prevs_add kernel/locking/lockdep.c:1980 [inline]
validate_chain kernel/locking/lockdep.c:2421 [inline]
__lock_acquire+0x3449/0x5020 kernel/locking/lockdep.c:3435
lock_acquire+0x1e4/0x540 kernel/locking/lockdep.c:3924
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+0x1e9/0x300 fs/super.c:1403
sb_start_write include/linux/fs.h:1554 [inline]
mnt_want_write+0x3f/0xc0 fs/namespace.c:386
path_removexattr+0xf0/0x210 fs/xattr.c:703
__do_sys_removexattr fs/xattr.c:719 [inline]
__se_sys_removexattr fs/xattr.c:716 [inline]
__x64_sys_removexattr+0x59/0x80 fs/xattr.c:716
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x455ab9
Code: 1d ba 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 eb b9 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fee4a211c68 EFLAGS: 00000246 ORIG_RAX: 00000000000000c5
RAX: ffffffffffffffda RBX: 00007fee4a2126d4 RCX: 0000000000455ab9
RDX: 0000000000000000 RSI: 0000000020000080 RDI: 0000000020000040
RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004bbc1c R14: 00000000004d0f48 R15: 0000000000000000
team0 (unregistering): Port device team_slave_1 removed
team0 (unregistering): Port device team_slave_0 removed
bond0 (unregistering): Releasing backup interface bond_slave_1
bond0 (unregistering): Releasing backup interface bond_slave_0
bond0 (unregistering): Released all slaves
netlink: 3 bytes leftover after parsing attributes in process
`syz-executor4'.
netlink: 3 bytes leftover after parsing attributes in process
`syz-executor3'.
netlink: 3 bytes leftover after parsing attributes in process
`syz-executor1'.
netlink: 3 bytes leftover after parsing attributes in process
`syz-executor2'.
netlink: 3 bytes leftover after parsing attributes in process
`syz-executor4'.
netlink: 3 bytes leftover after parsing attributes in process
`syz-executor2'.
netlink: 3 bytes leftover after parsing attributes in process
`syz-executor1'.
netlink: 3 bytes leftover after parsing attributes in process
`syz-executor4'.
netlink: 3 bytes leftover after parsing attributes in process
`syz-executor2'.
nla_parse: 16 callbacks suppressed
netlink: 3 bytes leftover after parsing attributes in process
`syz-executor4'.
netlink: 3 bytes leftover after parsing attributes in process
`syz-executor4'.
netlink: 3 bytes leftover after parsing attributes in process
`syz-executor4'.


---
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:
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syzbot.

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