Re: [syzbot] [bcachefs?] WARNING in closure_put_after_sub

On Wed, Jul 16, 2025 at 06:05:35PM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    3f31a806a62e Merge tag 'mm-hotfixes-stable-2025-07-11-16-1..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=116e1d82580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=b309c907eaab29da
> dashboard link: https://syzkaller.appspot.com/bug?extid=0ea2c41a649240197795
> compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-3f31a806.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/7304d62ced97/vmlinux-3f31a806.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/4913df6ab730/bzImage-3f31a806.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: [email protected]
> 
> ------------[ cut here ]------------
> closure has guard bits set: a8000000 (25)
> WARNING: CPU: 0 PID: 5328 at lib/closure.c:22 closure_put_after_sub_checks lib/closure.c:20 [inline]
> WARNING: CPU: 0 PID: 5328 at lib/closure.c:22 closure_put_after_sub+0x173/0x320 lib/closure.c:32
> Modules linked in:
> CPU: 0 UID: 0 PID: 5328 Comm: kworker/u5:2 Not tainted 6.16.0-rc5-syzkaller-00266-g3f31a806a62e #0 PREEMPT(full) 
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> Workqueue: bcachefs_journal journal_write_done
> RIP: 0010:closure_put_after_sub_checks lib/closure.c:20 [inline]
> RIP: 0010:closure_put_after_sub+0x173/0x320 lib/closure.c:32
> Code: c1 6e 50 ff cd 4c 89 f3 e9 c8 fe ff ff e8 85 f7 c9 fc 90 44 89 f0 48 0f bd d0 48 c7 c7 40 f5 e4 8b 44 89 fe e8 3e da 8d fc 90 <0f> 0b 90 90 e9 d0 fe ff ff e8 5f f7 c9 fc 90 89 ee 81 e6 00 00 00
> RSP: 0018:ffffc9000d5ef820 EFLAGS: 00010246
> RAX: 641034d4b1ecad00 RBX: ffffffff936402f0 RCX: ffff88801c734880
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000002
> RBP: 00000000efffffff R08: ffff88801fc24293 R09: 1ffff11003f84852
> R10: dffffc0000000000 R11: ffffed1003f84853 R12: dffffc0000000000
> R13: ffff88805324a9f0 R14: 0000000003ffffff R15: 00000000a8000000
> FS:  0000000000000000(0000) GS:ffff88808d21b000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000563f86c91bc0 CR3: 0000000033352000 CR4: 0000000000352ef0
> Call Trace:
>  <TASK>
>  closure_sub lib/closure.c:61 [inline]
>  __closure_wake_up+0x81/0xb0 lib/closure.c:91
>  closure_wake_up include/linux/closure.h:349 [inline]
>  journal_write_done+0x994/0x1270 fs/bcachefs/journal_io.c:1768
>  process_one_work kernel/workqueue.c:3238 [inline]
>  process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3321
>  worker_thread+0x8a0/0xda0 kernel/workqueue.c:3402
>  kthread+0x70e/0x8a0 kernel/kthread.c:464
>  ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>  </TASK>
> 
> 
> ---
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ec.c was returning with the passed-in closure on c->freelist_wait,
without returning an error that indicated we were blocking

#syz fix: bcachefs: Ensure we don't return with closure on waitlist