Re: [syzbot] [iomap?] WARNING in ifs_free

[Joanne Koong]

On Thu, Feb 19, 2026 at 12:51 PM syzbot
<syzbot+d3a62bea0e61f9d121da@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> syzbot has found a reproducer for the following issue on:
>
> HEAD commit:    2b7a25df823d Merge tag 'mm-nonmm-stable-2026-02-18-19-56' ..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=10c21722580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=65722f41f7edc17e
> dashboard link: https://syzkaller.appspot.com/bug?extid=d3a62bea0e61f9d121da
> compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1501dc02580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1357f652580000
>
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-2b7a25df.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/f3a54d09b17c/vmlinux-2b7a25df.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/fb704901bce5/bzImage-2b7a25df.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/b778b9903de5/mount_0.gz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+d3a62bea0e61f9d121da@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> ------------[ cut here ]------------
> ifs_is_fully_uptodate(folio, ifs) != folio_test_uptodate(folio)
> WARNING: fs/iomap/buffered-io.c:256 at ifs_free+0x358/0x420 fs/iomap/buffered-io.c:255, CPU#0: syz-executor/5453
> Modules linked in:
> CPU: 0 UID: 0 PID: 5453 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> RIP: 0010:ifs_free+0x358/0x420 fs/iomap/buffered-io.c:255
> Code: 41 5f 5d e9 7a fb bd ff e8 45 5a 5e ff 90 0f 0b 90 e9 d0 fe ff ff e8 37 5a 5e ff 90 0f 0b 90 e9 0a ff ff ff e8 29 5a 5e ff 90 <0f> 0b 90 eb c3 44 89 e1 80 e1 07 80 c1 03 38 c1 0f 8c 06 fe ff ff
> RSP: 0018:ffffc9000dfcf688 EFLAGS: 00010293
> RAX: ffffffff82674207 RBX: 0000000000000008 RCX: ffff88801f834900
> RDX: 0000000000000000 RSI: 0000000000000008 RDI: 0000000000000000
> RBP: 000000008267bc01 R08: ffffea00010fb747 R09: 1ffffd400021f6e8
> R10: dffffc0000000000 R11: fffff9400021f6e9 R12: ffff888051c7da44
> R13: ffff888051c7da00 R14: ffffea00010fb740 R15: 1ffffd400021f6e9
> FS:  0000555586def500(0000) GS:ffff88808ca5b000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000555586e0aa28 CR3: 00000000591fe000 CR4: 0000000000352ef0
> Call Trace:
>  <TASK>
>  folio_invalidate mm/truncate.c:140 [inline]
>  truncate_cleanup_folio+0xcb/0x190 mm/truncate.c:160
>  truncate_inode_pages_range+0x2ce/0xe30 mm/truncate.c:404
>  ntfs_evict_inode+0x19/0x40 fs/ntfs3/inode.c:1861
>  evict+0x61e/0xb10 fs/inode.c:846
>  dispose_list fs/inode.c:888 [inline]
>  evict_inodes+0x75a/0x7f0 fs/inode.c:942
>  generic_shutdown_super+0xaa/0x2d0 fs/super.c:632
>  kill_block_super+0x44/0x90 fs/super.c:1725
>  ntfs3_kill_sb+0x44/0x1c0 fs/ntfs3/super.c:1889
>  deactivate_locked_super+0xbc/0x130 fs/super.c:476
>  cleanup_mnt+0x437/0x4d0 fs/namespace.c:1312
>  task_work_run+0x1d9/0x270 kernel/task_work.c:233
>  resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
>  __exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
>  exit_to_user_mode_loop+0xed/0x480 kernel/entry/common.c:98
>  __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
>  syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
>  syscall_exit_to_user_mode include/linux/entry-common.h:325 [inline]
>  do_syscall_64+0x32d/0xf80 arch/x86/entry/syscall_64.c:100
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7fb0f859d897
> Code: a2 c7 05 5c ee 24 00 00 00 00 00 eb 96 e8 e1 12 00 00 90 31 f6 e9 09 00 00 00 66 0f 1f 84 00 00 00 00 00 b8 a6 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 01 c3 48 c7 c2 e8 ff ff ff f7 d8 64 89 02 b8
> RSP: 002b:00007ffd23732b28 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
> RAX: 0000000000000000 RBX: 00007fb0f8631ef0 RCX: 00007fb0f859d897
> RDX: 0000000000000000 RSI: 0000000000000009 RDI: 00007ffd23732be0
> RBP: 00007ffd23732be0 R08: 00007ffd23733be0 R09: 00000000ffffffff
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffd23733c70
> R13: 00007fb0f8631ef0 R14: 000000000001b126 R15: 00007ffd23733cb0
>  </TASK>
>

I ran the repro locally to see if it's the same issue fixed by [1] but
this is a different unrelated issue.

The folio is uptodate but the ifs uptodate bitmap is not reflected as
fully uptodate. I think this is because ntfs3 handles writes for
compressed files through its own interface that doesn't go through
iomap where it calls folio_mark_uptodate() but the ifs bitmap doesn't
get updated. fuse-blk servers that operate in writethrough mode run
into something like this as well [2].

This doesn't lead to any data corruption issues. Should we get rid of
the  WARN_ON_ONCE(ifs_is_fully_uptodate(folio, ifs) !=
folio_test_uptodate(folio))? The alternative is to make a modified
version of the functionality in "iomap_set_range_uptodate()" a public
api callable by subsystems.

Thanks,
Joanne

[1] https://lore.kernel.org/linux-fsdevel/20260219003911.344478-1-joannelkoong@xxxxxxxxx/
[2] https://lore.kernel.org/linux-fsdevel/20251223223018.3295372-2-sashal@xxxxxxxxxx/