Re: [syzbot] [btrfs?] BUG: spinlock bad magic in btrfs_stop_all_workers

[David Sterba]

On Tue, Jun 18, 2024 at 02:43:21PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    2ccbdf43d5e7 Merge tag 'for-linus' of git://git.kernel.org..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=10bf1a61980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=81c0d76ceef02b39
> dashboard link: https://syzkaller.appspot.com/bug?extid=9bf5c83263a4d4387899
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> userspace arch: i386
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7bc7510fe41f/non_bootable_disk-2ccbdf43.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/13cdb5bfbafa/vmlinux-2ccbdf43.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/7a14f5d07f81/bzImage-2ccbdf43.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+9bf5c83263a4d4387899@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> BTRFS info (device loop3): last unmount of filesystem 3a492a15-ac49-4ce6-945e-cef7a687c6c9
> BUG: spinlock bad magic on CPU#0, syz-executor.3/7928
> ==================================================================
> BUG: KASAN: slab-out-of-bounds in task_pid_nr include/linux/pid.h:232 [inline]
> BUG: KASAN: slab-out-of-bounds in spin_dump kernel/locking/spinlock_debug.c:64 [inline]
> BUG: KASAN: slab-out-of-bounds in spin_bug+0x17d/0x1d0 kernel/locking/spinlock_debug.c:78
> Read of size 4 at addr ffff888028b23dd8 by task syz-executor.3/7928

Most likely this was a side effect of bug fixed by commit f3a5367c679d
("btrfs: protect folio::private when attaching extent buffer folios").
The timeframe corresponds with increased number of bogus errors caused by
use-after-free of a page.

The fix is best guess.

#syz fix: btrfs: protect folio::private when attaching extent buffer folios