Message-ID: <aXX5tl7lvc-SdUKN@li-dc0c254c-257c-11b2-a85c-98b6c1322444.ibm.com>
Date: Sun, 25 Jan 2026 16:38:38 +0530
From: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To: syzbot <syzbot+e625b79bfdd66c067432@...kaller.appspotmail.com>
Cc: adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        tytso@....edu
Subject: Re: [syzbot] [ext4?] WARNING in ext4_split_convert_extents

On Fri, Jan 23, 2026 at 05:27:22PM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    d08c85ac8894 Add linux-next specific files for 20260119
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=171a1852580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=ee3bfbe9e319ed0c
> dashboard link: https://syzkaller.appspot.com/bug?extid=e625b79bfdd66c067432
> compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=121533fa580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12bc7b9a580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/94cfdbd8a0c9/disk-d08c85ac.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/f7ec0695ac29/vmlinux-d08c85ac.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/ddc8307e03e3/bzImage-d08c85ac.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/6ddc9a8efbb6/mount_0.gz
>   fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=14f96bfc580000)
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+e625b79bfdd66c067432@...kaller.appspotmail.com
> 
> ------------[ cut here ]------------
> WARNING: fs/ext4/extents.c:3486 at ext4_split_extent fs/ext4/extents.c:3485 [inline], CPU#1: kworker/u8:4/58
> WARNING: fs/ext4/extents.c:3486 at ext4_split_convert_extents+0x13c2/0x1a10 fs/ext4/extents.c:3839, CPU#1: kworker/u8:4/58
> Modules linked in:
> CPU: 1 UID: 0 PID: 58 Comm: kworker/u8:4 Not tainted syzkaller #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
> Workqueue: ext4-rsv-conversion ext4_end_io_rsv_work
> RIP: 0010:ext4_split_extent fs/ext4/extents.c:3485 [inline]
> RIP: 0010:ext4_split_convert_extents+0x13c2/0x1a10 fs/ext4/extents.c:3839
> Code: 4c 8b 44 24 38 e8 be 85 fe ff 40 b5 01 4c 8b 64 24 18 49 81 fc 00 f0 ff ff 0f 87 19 ff ff ff e9 4e f0 ff ff e8 3f 8f 4a ff 90 <0f> 0b 90 49 bf 00 00 00 00 00 fc ff df 44 8b 6c 24 04 4c 8b 64 24
> RSP: 0018:ffffc900015f7328 EFLAGS: 00010293
> RAX: ffffffff82768aa1 RBX: dffffc0000000001 RCX: ffff88801cb99e40
> RDX: 0000000000000000 RSI: 0000000000000100 RDI: 0000000000000008
> RBP: 0000000000000008 R08: ffff88802ba1269f R09: 0000000000000000
> R10: ffff88802ba12690 R11: ffffed10057424d4 R12: 0000000000000010
> R13: ffff888073634d01 R14: 0000000000000010 R15: 0000000000000100
> FS:  0000000000000000(0000) GS:ffff888125cf2000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000200000000080 CR3: 000000000df3e000 CR4: 00000000003526f0
> Call Trace:
>  <TASK>
>  ext4_convert_unwritten_extents_endio fs/ext4/extents.c:3915 [inline]
>  ext4_ext_handle_unwritten_extents fs/ext4/extents.c:3999 [inline]
>  ext4_ext_map_blocks+0xde4/0x5560 fs/ext4/extents.c:4336
>  ext4_map_create_blocks+0x11d/0x540 fs/ext4/inode.c:616
>  ext4_map_blocks+0x759/0x1170 fs/ext4/inode.c:809
>  ext4_convert_unwritten_extents+0x2a8/0x5d0 fs/ext4/extents.c:5038
>  ext4_convert_unwritten_io_end_vec+0xff/0x170 fs/ext4/extents.c:5078
>  ext4_end_io_end+0xc7/0x410 fs/ext4/page-io.c:200
>  ext4_do_flush_completed_IO fs/ext4/page-io.c:291 [inline]
>  ext4_end_io_rsv_work+0x262/0x330 fs/ext4/page-io.c:306
>  process_one_work+0x93a/0x15a0 kernel/workqueue.c:3279
>  process_scheduled_works kernel/workqueue.c:3362 [inline]
>  worker_thread+0x9b0/0xee0 kernel/workqueue.c:3443
>  kthread+0x389/0x480 kernel/kthread.c:467
>  ret_from_fork+0x510/0xa50 arch/x86/kernel/process.c:158
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>  </TASK>

Okay so I looked into this report. I see that it is not hitting in
lastest linux-next but only in commit d08c85ac8894 in linux-next.
Looking at the code, this commit has an older v2 of the patches which
had an issue where we were not updating orig_* variables in
ext4_split_extent() causing this WARN. This has been fixed in v3
onwards, which seems to be the version that the lastest linux-next has
hence we don't hit this anymore.

Regards,
ojaswin

> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
> 
> syzbot will keep track of this issue. See:
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> 
> If the report is already addressed, let syzbot know by replying with:
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> 
> If you want syzbot to run the reproducer, reply with:
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> If you attach or paste a git patch, syzbot will apply it before testing.
> 
> If you want to overwrite report's subsystems, reply with:
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> 
> If the report is a duplicate of another one, reply with:
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> 
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