Re: [syzbot] [bcachefs?] possible deadlock in bch2_symlink

[syzbot <syzbot+7836a68852a10ec3d790@syzkaller.appspotmail.com>]

syzbot has found a reproducer for the following issue on:

HEAD commit:    7ee983c850b4 Merge tag 'drm-fixes-2025-02-08' of https://g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17375ca4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=1909f2f0d8e641ce
dashboard link: https://syzkaller.appspot.com/bug?extid=7836a68852a10ec3d790
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14e0cca4580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=155361b0580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-7ee983c8.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f2f78699fc41/vmlinux-7ee983c8.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ca55e6e8dd01/bzImage-7ee983c8.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/aa79c539b21d/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+7836a68852a10ec3d790@syzkaller.appspotmail.com

bcachefs (loop0): reading snapshots table
bcachefs (loop0): reading snapshots done
bcachefs (loop0): done starting filesystem
============================================
WARNING: possible recursive locking detected
6.14.0-rc1-syzkaller-00181-g7ee983c850b4 #0 Not tainted
--------------------------------------------
syz-executor294/5305 is trying to acquire lock:
ffff888044775078 (&sb->s_type->i_mutex_key#16){++++}-{4:4}, at: inode_lock include/linux/fs.h:877 [inline]
ffff888044775078 (&sb->s_type->i_mutex_key#16){++++}-{4:4}, at: bch2_symlink+0x176/0x310 fs/bcachefs/fs.c:839

but task is already holding lock:
ffff888044774148 (&sb->s_type->i_mutex_key#16){++++}-{4:4}, at: inode_lock include/linux/fs.h:877 [inline]
ffff888044774148 (&sb->s_type->i_mutex_key#16){++++}-{4:4}, at: ovl_copy_up_workdir fs/overlayfs/copy_up.c:782 [inline]
ffff888044774148 (&sb->s_type->i_mutex_key#16){++++}-{4:4}, at: ovl_do_copy_up fs/overlayfs/copy_up.c:1001 [inline]
ffff888044774148 (&sb->s_type->i_mutex_key#16){++++}-{4:4}, at: ovl_copy_up_one fs/overlayfs/copy_up.c:1202 [inline]
ffff888044774148 (&sb->s_type->i_mutex_key#16){++++}-{4:4}, at: ovl_copy_up_flags+0x19cb/0x47c0 fs/overlayfs/copy_up.c:1257

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&sb->s_type->i_mutex_key#16);
  lock(&sb->s_type->i_mutex_key#16);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

7 locks held by syz-executor294/5305:
 #0: ffff88801df94420 (sb_writers#10){.+.+}-{0:0}, at: mnt_want_write+0x3f/0x90 fs/namespace.c:547
 #1: ffff88804470de50 (&ovl_i_mutex_dir_key[depth]/1){+.+.}-{4:4}, at: inode_lock_nested include/linux/fs.h:912 [inline]
 #1: ffff88804470de50 (&ovl_i_mutex_dir_key[depth]/1){+.+.}-{4:4}, at: lock_rename fs/namei.c:3217 [inline]
 #1: ffff88804470de50 (&ovl_i_mutex_dir_key[depth]/1){+.+.}-{4:4}, at: do_renameat2+0x62c/0x13f0 fs/namei.c:5161
 #2: ffff88804470e418 (&ovl_i_mutex_key[depth]){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:877 [inline]
 #2: ffff88804470e418 (&ovl_i_mutex_key[depth]){+.+.}-{4:4}, at: lock_two_nondirectories+0xe1/0x170 fs/inode.c:1281
 #3: ffff88804470e9e0 (&ovl_i_mutex_key[depth]/4){+.+.}-{4:4}, at: vfs_rename+0x6a2/0xf00 fs/namei.c:5040
 #4: ffff88804470e7d0 (&ovl_i_lock_key[depth]){+.+.}-{4:4}, at: ovl_inode_lock_interruptible fs/overlayfs/overlayfs.h:650 [inline]
 #4: ffff88804470e7d0 (&ovl_i_lock_key[depth]){+.+.}-{4:4}, at: ovl_copy_up_start+0x53/0x310 fs/overlayfs/util.c:727
 #5: ffff8880477b0420 (sb_writers#9){.+.+}-{0:0}, at: ovl_copy_up_workdir fs/overlayfs/copy_up.c:781 [inline]
 #5: ffff8880477b0420 (sb_writers#9){.+.+}-{0:0}, at: ovl_do_copy_up fs/overlayfs/copy_up.c:1001 [inline]
 #5: ffff8880477b0420 (sb_writers#9){.+.+}-{0:0}, at: ovl_copy_up_one fs/overlayfs/copy_up.c:1202 [inline]
 #5: ffff8880477b0420 (sb_writers#9){.+.+}-{0:0}, at: ovl_copy_up_flags+0x19b4/0x47c0 fs/overlayfs/copy_up.c:1257
 #6: ffff888044774148 (&sb->s_type->i_mutex_key#16){++++}-{4:4}, at: inode_lock include/linux/fs.h:877 [inline]
 #6: ffff888044774148 (&sb->s_type->i_mutex_key#16){++++}-{4:4}, at: ovl_copy_up_workdir fs/overlayfs/copy_up.c:782 [inline]
 #6: ffff888044774148 (&sb->s_type->i_mutex_key#16){++++}-{4:4}, at: ovl_do_copy_up fs/overlayfs/copy_up.c:1001 [inline]
 #6: ffff888044774148 (&sb->s_type->i_mutex_key#16){++++}-{4:4}, at: ovl_copy_up_one fs/overlayfs/copy_up.c:1202 [inline]
 #6: ffff888044774148 (&sb->s_type->i_mutex_key#16){++++}-{4:4}, at: ovl_copy_up_flags+0x19cb/0x47c0 fs/overlayfs/copy_up.c:1257

stack backtrace:
CPU: 0 UID: 0 PID: 5305 Comm: syz-executor294 Not tainted 6.14.0-rc1-syzkaller-00181-g7ee983c850b4 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_deadlock_bug+0x483/0x620 kernel/locking/lockdep.c:3039
 check_deadlock kernel/locking/lockdep.c:3091 [inline]
 validate_chain+0x15e2/0x5920 kernel/locking/lockdep.c:3893
 __lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5228
 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851
 down_write+0x99/0x220 kernel/locking/rwsem.c:1577
 inode_lock include/linux/fs.h:877 [inline]
 bch2_symlink+0x176/0x310 fs/bcachefs/fs.c:839
 vfs_symlink+0x137/0x2e0 fs/namei.c:4671
 ovl_do_symlink+0x85/0xd0 fs/overlayfs/overlayfs.h:267
 ovl_create_real+0x346/0x550 fs/overlayfs/dir.c:206
 ovl_copy_up_workdir fs/overlayfs/copy_up.c:783 [inline]
 ovl_do_copy_up fs/overlayfs/copy_up.c:1001 [inline]
 ovl_copy_up_one fs/overlayfs/copy_up.c:1202 [inline]
 ovl_copy_up_flags+0x19fe/0x47c0 fs/overlayfs/copy_up.c:1257
 ovl_rename+0x62a/0x1760 fs/overlayfs/dir.c:1150
 vfs_rename+0xbdb/0xf00 fs/namei.c:5069
 do_renameat2+0xd94/0x13f0 fs/namei.c:5226
 __do_sys_rename fs/namei.c:5273 [inline]
 __se_sys_rename fs/namei.c:5271 [inline]
 __x64_sys_rename+0x82/0x90 fs/namei.c:5271
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f0d8dddad19
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 17 00 00 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 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd9dbea2d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000052
RAX: ffffffffffffffda RBX: 0031656c69662f2e RCX: 00007f0d8dddad19
RDX: 00007f0d8dddad19 RSI: 0000400000000840 RDI: 0000400000000800
RBP: 0031656c69662f2e R08: 000055558454d4c0 R09: 000055558454d4c0
R10: 000055558454d4c0 R11: 0000000000000246 R12: 00007ffd9dbea300
R13: 00007ffd9dbea528 R14: 431bde82d7b634db R15: 00007f0d8de2303b
 </TASK>
syz-executor294 (5305) used greatest stack depth: 10768 bytes left


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