Re: [syzbot] [ext4?] possible deadlock in ext4_find_inline_entry

syzbot
2022-12-29T01:24:15Z

possible deadlock in ext4_xattr_set_entry

EXT4-fs: Warning: mounting with an experimental mount option 'dioread_nolock' for blocksize < PAGE_SIZE
EXT4-fs (loop0): mounted filesystem without journal. Quota mode: none.
======================================================
WARNING: possible circular locking dependency detected
6.1.0-rc8-syzkaller-00172-ga5541c0811a0-dirty #0 Not tainted
------------------------------------------------------
syz-executor.0/3668 is trying to acquire lock:
ffff0000cf16bd60 (&sb->s_type->i_mutex_key#8){++++}-{3:3}, at: inode_lock include/linux/fs.h:756 [inline]
ffff0000cf16bd60 (&sb->s_type->i_mutex_key#8){++++}-{3:3}, at: ext4_xattr_inode_create fs/ext4/xattr.c:1453 [inline]
ffff0000cf16bd60 (&sb->s_type->i_mutex_key#8){++++}-{3:3}, at: ext4_xattr_inode_lookup_create fs/ext4/xattr.c:1536 [inline]
ffff0000cf16bd60 (&sb->s_type->i_mutex_key#8){++++}-{3:3}, at: ext4_xattr_set_entry+0xdbc/0xe00 fs/ext4/xattr.c:1664

but task is already holding lock:
ffff0000cf16b098 (&ei->xattr_sem){++++}-{3:3}, at: ext4_write_lock_xattr fs/ext4/xattr.h:155 [inline]
ffff0000cf16b098 (&ei->xattr_sem){++++}-{3:3}, at: ext4_xattr_set_handle+0xd0/0x9a0 fs/ext4/xattr.c:2308

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&ei->xattr_sem){++++}-{3:3}:
down_read+0x5c/0x78 kernel/locking/rwsem.c:1509
ext4_xattr_get+0x90/0x418 fs/ext4/xattr.c:665
ext4_xattr_security_get+0x40/0x54 fs/ext4/xattr_security.c:20
__vfs_getxattr+0x1fc/0x20c fs/xattr.c:407
cap_inode_need_killpriv+0x34/0x5c security/commoncap.c:301
security_inode_need_killpriv+0x34/0x88 security/security.c:1422
dentry_needs_remove_privs fs/inode.c:1995 [inline]
__file_remove_privs+0xe0/0x308 fs/inode.c:2026
file_modified_flags+0x60/0x330 fs/inode.c:2148
file_modified+0x24/0x34 fs/inode.c:2177
ext4_write_checks fs/ext4/file.c:264 [inline]
ext4_buffered_write_iter+0x12c/0x294 fs/ext4/file.c:280
ext4_file_write_iter+0x84/0x408 fs/ext4/file.c:700
call_write_iter include/linux/fs.h:2199 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x2dc/0x46c fs/read_write.c:584
ksys_write+0xb4/0x160 fs/read_write.c:637
__do_sys_write fs/read_write.c:649 [inline]
__se_sys_write fs/read_write.c:646 [inline]
__arm64_sys_write+0x24/0x34 fs/read_write.c:646
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x48/0x140 arch/arm64/kernel/syscall.c:197
el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

-> #0 (&sb->s_type->i_mutex_key#8){++++}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3097 [inline]
check_prevs_add kernel/locking/lockdep.c:3216 [inline]
validate_chain kernel/locking/lockdep.c:3831 [inline]
__lock_acquire+0x1530/0x3084 kernel/locking/lockdep.c:5055
lock_acquire+0x100/0x1f8 kernel/locking/lockdep.c:5668
down_write+0x5c/0x88 kernel/locking/rwsem.c:1562
inode_lock include/linux/fs.h:756 [inline]
ext4_xattr_inode_create fs/ext4/xattr.c:1453 [inline]
ext4_xattr_inode_lookup_create fs/ext4/xattr.c:1536 [inline]
ext4_xattr_set_entry+0xdbc/0xe00 fs/ext4/xattr.c:1664
ext4_xattr_ibody_set+0x94/0x184 fs/ext4/xattr.c:2224
ext4_xattr_set_handle+0x648/0x9a0 fs/ext4/xattr.c:2381
ext4_xattr_set+0x100/0x1d0 fs/ext4/xattr.c:2495
ext4_xattr_trusted_set+0x4c/0x64 fs/ext4/xattr_trusted.c:38
__vfs_setxattr+0x250/0x260 fs/xattr.c:182
__vfs_setxattr_noperm+0xcc/0x320 fs/xattr.c:216
__vfs_setxattr_locked+0x16c/0x194 fs/xattr.c:277
vfs_setxattr+0xf4/0x1f4 fs/xattr.c:309
do_setxattr fs/xattr.c:594 [inline]
setxattr fs/xattr.c:617 [inline]
path_setxattr+0x354/0x414 fs/xattr.c:636
__do_sys_lsetxattr fs/xattr.c:659 [inline]
__se_sys_lsetxattr fs/xattr.c:655 [inline]
__arm64_sys_lsetxattr+0x2c/0x40 fs/xattr.c:655
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x48/0x140 arch/arm64/kernel/syscall.c:197
el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&ei->xattr_sem);
lock(&sb->s_type->i_mutex_key#8);
lock(&ei->xattr_sem);
lock(&sb->s_type->i_mutex_key#8);

*** DEADLOCK ***

3 locks held by syz-executor.0/3668:
#0: ffff0000c9dee460 (sb_writers#3){.+.+}-{0:0}, at: mnt_want_write+0x20/0x64 fs/namespace.c:393
#1: ffff0000cf16b3d0 (&type->i_mutex_dir_key#3){++++}-{3:3}, at: inode_lock include/linux/fs.h:756 [inline]
#1: ffff0000cf16b3d0 (&type->i_mutex_dir_key#3){++++}-{3:3}, at: vfs_setxattr+0xd4/0x1f4 fs/xattr.c:308
#2: ffff0000cf16b098 (&ei->xattr_sem){++++}-{3:3}, at: ext4_write_lock_xattr fs/ext4/xattr.h:155 [inline]
#2: ffff0000cf16b098 (&ei->xattr_sem){++++}-{3:3}, at: ext4_xattr_set_handle+0xd0/0x9a0 fs/ext4/xattr.c:2308

stack backtrace:
CPU: 1 PID: 3668 Comm: syz-executor.0 Not tainted 6.1.0-rc8-syzkaller-00172-ga5541c0811a0-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Call trace:
dump_backtrace+0x1c4/0x1f0 arch/arm64/kernel/stacktrace.c:156
show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:163
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x104/0x16c lib/dump_stack.c:106
dump_stack+0x1c/0x58 lib/dump_stack.c:113
print_circular_bug+0x2c4/0x2c8 kernel/locking/lockdep.c:2055
check_noncircular+0x14c/0x154 kernel/locking/lockdep.c:2177
check_prev_add kernel/locking/lockdep.c:3097 [inline]
check_prevs_add kernel/locking/lockdep.c:3216 [inline]
validate_chain kernel/locking/lockdep.c:3831 [inline]
__lock_acquire+0x1530/0x3084 kernel/locking/lockdep.c:5055
lock_acquire+0x100/0x1f8 kernel/locking/lockdep.c:5668
down_write+0x5c/0x88 kernel/locking/rwsem.c:1562
inode_lock include/linux/fs.h:756 [inline]
ext4_xattr_inode_create fs/ext4/xattr.c:1453 [inline]
ext4_xattr_inode_lookup_create fs/ext4/xattr.c:1536 [inline]
ext4_xattr_set_entry+0xdbc/0xe00 fs/ext4/xattr.c:1664
ext4_xattr_ibody_set+0x94/0x184 fs/ext4/xattr.c:2224
ext4_xattr_set_handle+0x648/0x9a0 fs/ext4/xattr.c:2381
ext4_xattr_set+0x100/0x1d0 fs/ext4/xattr.c:2495
ext4_xattr_trusted_set+0x4c/0x64 fs/ext4/xattr_trusted.c:38
__vfs_setxattr+0x250/0x260 fs/xattr.c:182
__vfs_setxattr_noperm+0xcc/0x320 fs/xattr.c:216
__vfs_setxattr_locked+0x16c/0x194 fs/xattr.c:277
vfs_setxattr+0xf4/0x1f4 fs/xattr.c:309
do_setxattr fs/xattr.c:594 [inline]
setxattr fs/xattr.c:617 [inline]
path_setxattr+0x354/0x414 fs/xattr.c:636
__do_sys_lsetxattr fs/xattr.c:659 [inline]
__se_sys_lsetxattr fs/xattr.c:655 [inline]
__arm64_sys_lsetxattr+0x2c/0x40 fs/xattr.c:655
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x48/0x140 arch/arm64/kernel/syscall.c:197
el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:637
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:584

Tested on:

commit: a5541c08 Merge branch 'for-next/core' into for-kernelci
git tree: https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=16f5d4bc480000
kernel config: https://syzkaller.appspot.com/x/.config?x=cbd4e584773e9397
dashboard link: https://syzkaller.appspot.com/bug?extid=d3bb749184481f92deb5
compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
userspace arch: arm64
patch: https://syzkaller.appspot.com/x/patch.diff?x=15be6de4480000