[syzbot] [gfs2?] KASAN: null-ptr-deref Read in gfs2_drop_inode

[syzbot <syzbot+b12826218502df019f9d@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    176e917e010c Add linux-next specific files for 20250523
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=135065f4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e7902c752bef748
dashboard link: https://syzkaller.appspot.com/bug?extid=b12826218502df019f9d
compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=151759f4580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16b9c5f4580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/5f7692c642fa/disk-176e917e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/057a442d42d0/vmlinux-176e917e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/8f8ebdb4dd96/bzImage-176e917e.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/0e694bf0a04e/mount_0.gz
  fsck result: OK (log: https://syzkaller.appspot.com/x/fsck.log?x=16e42170580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b12826218502df019f9d@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: null-ptr-deref in instrument_atomic_read include/linux/instrumented.h:68 [inline]
BUG: KASAN: null-ptr-deref in _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
BUG: KASAN: null-ptr-deref in gfs2_drop_inode+0x20c/0x3a0 fs/gfs2/super.c:1052
Read of size 8 at addr 00000000000000a8 by task syz-executor628/5863

CPU: 0 UID: 0 PID: 5863 Comm: syz-executor628 Not tainted 6.15.0-rc7-next-20250523-syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 kasan_report+0x118/0x150 mm/kasan/report.c:634
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x2b0/0x2c0 mm/kasan/generic.c:189
 instrument_atomic_read include/linux/instrumented.h:68 [inline]
 _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
 gfs2_drop_inode+0x20c/0x3a0 fs/gfs2/super.c:1052
 iput_final fs/inode.c:1868 [inline]
 iput+0x45d/0x9d0 fs/inode.c:1924
 gfs2_fill_super+0x1418/0x2010 fs/gfs2/ops_fstype.c:1314
 get_tree_bdev_flags+0x40b/0x4d0 fs/super.c:1679
 gfs2_get_tree+0x51/0x1e0 fs/gfs2/ops_fstype.c:1333
 vfs_get_tree+0x92/0x2b0 fs/super.c:1802
 do_new_mount+0x24a/0xa40 fs/namespace.c:3869
 do_mount fs/namespace.c:4206 [inline]
 __do_sys_mount fs/namespace.c:4417 [inline]
 __se_sys_mount+0x317/0x410 fs/namespace.c:4394
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f219bad284a
Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb a6 e8 6e 07 00 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 49 89 ca b8 a5 00 00 00 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:00007ffdb657b2f8 EFLAGS: 00000282 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f219bad284a
RDX: 0000200000021140 RSI: 0000200000021180 RDI: 00007ffdb657b350
RBP: 0000000000000004 R08: 00007ffdb657b390 R09: 0000000000021135
R10: 0000000000000000 R11: 0000000000000282 R12: 0000000001000000
R13: 00007ffdb657b390 R14: 0000200000021180 R15: 0000000000000003
 </TASK>
==================================================================


---
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