Re: [moderation/CI] Re: ext4: convert pa_count from atomic_t to refcount_t

#syz upstream

On Mon, Jul 20, 2026 at 7:44 AM syzbot ci
<[email protected]> wrote:
>
> syzbot ci has tested the following series
>
> [v1] ext4: convert pa_count from atomic_t to refcount_t
> https://lore.kernel.org/all/[email protected]
> * [PATCH] ext4: convert pa_count from atomic_t to refcount_t
>
> and found the following issue:
> WARNING: refcount bug in ext4_mb_use_preallocated
>
> Full report is available here:
> https://ci.syzbot.org/series/34fda797-e979-409c-bc2d-7af3e163df14
>
> ***
>
> WARNING: refcount bug in ext4_mb_use_preallocated
>
> tree:      torvalds
> URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux
> base:      1590cf0329716306e948a8fc29f1d3ee87d3989f
> arch:      amd64
> compiler:  Debian clang version 22.1.6 (++20260514074242+fc4aad7b5db3-1~exp1~20260514074407.73), Debian LLD 22.1.6
> config:    https://ci.syzbot.org/builds/05fa6c1d-a594-4691-ace3-ded3fc2ca4dc/config
>
> ------------[ cut here ]------------
> refcount_t: addition on 0; use-after-free.
> WARNING: lib/refcount.c:25 at refcount_warn_saturate+0x9f/0x110, CPU#0: kworker/u9:2/51
> Modules linked in:
> CPU: 0 UID: 0 PID: 51 Comm: kworker/u9:2 Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> Workqueue: writeback wb_workfn (flush-8:0)
> RIP: 0010:refcount_warn_saturate+0x9f/0x110
> Code: eb 66 85 db 74 3e 83 fb 01 75 4c e8 8b 73 0c fd 48 8d 3d 34 58 84 0b 67 48 0f b9 3a eb 4a e8 78 73 0c fd 48 8d 3d 31 58 84 0b <67> 48 0f b9 3a eb 37 e8 65 73 0c fd 48 8d 3d 2e 58 84 0b 67 48 0f
> RSP: 0018:ffffc90000bb6590 EFLAGS: 00010293
> RAX: ffffffff84b9ee08 RBX: 0000000000000002 RCX: ffff8881072a8000
> RDX: 0000000000000000 RSI: ffffffff8f126800 RDI: ffffffff903e4640
> RBP: ffff888112257dd0 R08: ffff8881072a8000 R09: 0000000000000005
> R10: 0000000000000004 R11: 0000000000000000 R12: dffffc0000000000
> R13: ffff888112257d98 R14: ffff888112257e10 R15: 0000000000000008
> FS:  0000000000000000(0000) GS:ffff88818dc15000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fc831b2c080 CR3: 0000000112724000 CR4: 00000000000006f0
> Call Trace:
>  <TASK>
>  ext4_mb_use_preallocated+0xaa0/0x14e0
>  ext4_mb_new_blocks+0x5a0/0x4560
>  ext4_ext_map_blocks+0x1534/0x5850
>  ext4_map_create_blocks+0x116/0x530
>  ext4_map_blocks+0x7e4/0x1240
>  ext4_do_writepages+0x23d3/0x47a0
>  ext4_writepages+0x241/0x3b0
>  do_writepages+0x338/0x560
>  __writeback_single_inode+0x12e/0xf90
>  writeback_sb_inodes+0x9de/0x1b00
>  __writeback_inodes_wb+0x114/0x240
>  wb_writeback+0x42f/0xad0
>  wb_workfn+0x980/0x10f0
>  process_scheduled_works+0xa8e/0x14e0
>  worker_thread+0xa47/0xfb0
>  kthread+0x388/0x470
>  ret_from_fork+0x514/0xb70
>  ret_from_fork_asm+0x1a/0x30
>  </TASK>
>
>
> ***
>
> If these findings have caused you to resend the series or submit a
> separate fix, please add the following tag to your commit message:
>   Tested-by: [email protected]
>
> ---
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