linux-ext4 - Re: [syzbot] [ext4?] kernel BUG in ext4_es_cache

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Message-ID: <aYsltA41z7B23GVN@li-dc0c254c-257c-11b2-a85c-98b6c1322444.ibm.com>
Date: Tue, 10 Feb 2026 18:03:56 +0530
From: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To: syzbot <syzbot+ccf1421545dbe5caa20c@...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?] kernel BUG in ext4_es_cache_extent (4)

On Mon, Feb 09, 2026 at 10:20:03PM -0800, syzbot wrote:
> Hello,
> 
> syzbot has tested the proposed patch but the reproducer is still triggering an issue:
> kernel BUG in ext4_es_cache_extent
> 
> EXT4-fs warning (device loop7): ext4_es_cache_extent:1081: inode #18: comm syz.7.209: ES cache extent failed: add [33,3,18446744073709551615,0x8] conflict with existing [33,15,257,0x2]
> EXT4-fs warning (device loop7): ext4_es_cache_extent:1081: inode #18: comm syz.7.209: ES cache extent failed: add [36,12,292,0x1] conflict with existing [33,15,257,0x2]
> ------------[ cut here ]------------
> kernel BUG at fs/ext4/extents_status.c:1043!
> Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
> CPU: 1 UID: 0 PID: 9040 Comm: syz.7.209 Not tainted syzkaller #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
> RIP: 0010:ext4_es_cache_extent+0x86e/0x990 fs/ext4/extents_status.c:1043
> Code: e1 07 80 c1 03 38 c1 0f 8c 5d fe ff ff 48 8b 7c 24 20 e8 25 4d af ff e9 4e fe ff ff e8 1b 12 47 ff 90 0f 0b e8 13 12 47 ff 90 <0f> 0b 65 8b 1d 9d 73 6e 10 bf 07 00 00 00 89 de e8 3d 16 47 ff 83
> RSP: 0018:ffffc900054fdba0 EFLAGS: 00010293
> RAX: ffffffff827d2c8d RBX: 0000000000000023 RCX: ffff88801dfe8000
> RDX: 0000000000000000 RSI: 0000000000000030 RDI: 0000000000000023
> RBP: ffffc900054fdce8 R08: ffffc900054fdc57 R09: 0000000000000000
> R10: ffffc900054fdc40 R11: fffff52000a9fb8b R12: 0000000000000030
> R13: dffffc0000000000 R14: 000000000000000f R15: ffff88807d100638
> FS:  00007efd221aa6c0(0000) GS:ffff888125866000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fbc5c5e8600 CR3: 000000007569c000 CR4: 00000000003526f0
> Call Trace:
>  <TASK>
>  ext4_cache_extents fs/ext4/extents.c:544 [inline]
>  __read_extent_tree_block+0x4b4/0x840 fs/ext4/extents.c:591
>  ext4_find_extent+0x76b/0xcc0 fs/ext4/extents.c:944
>  ext4_ext_map_blocks+0x29d/0x6cd0 fs/ext4/extents.c:4239
>  ext4_map_create_blocks fs/ext4/inode.c:613 [inline]
>  ext4_map_blocks+0x8da/0x1830 fs/ext4/inode.c:816
>  _ext4_get_block+0x1e3/0x470 fs/ext4/inode.c:916
>  ext4_get_block_unwritten+0x2e/0x100 fs/ext4/inode.c:949
>  ext4_block_write_begin+0xb14/0x1950 fs/ext4/inode.c:1203
>  ext4_write_begin+0xb40/0x1870 fs/ext4/ext4_jbd2.h:-1
>  ext4_da_write_begin+0x355/0xd30 fs/ext4/inode.c:3130
>  generic_perform_write+0x2e2/0x8f0 mm/filemap.c:4314
>  ext4_buffered_write_iter+0xce/0x3a0 fs/ext4/file.c:299
>  ext4_file_write_iter+0x298/0x1c10 fs/ext4/file.c:-1
>  __kernel_write_iter+0x41e/0x880 fs/read_write.c:619
>  dump_emit_page fs/coredump.c:1298 [inline]
>  dump_user_range+0xb89/0x12d0 fs/coredump.c:1372
>  elf_core_dump+0x34c2/0x3ad0 fs/binfmt_elf.c:2111
>  coredump_write+0x1219/0x1950 fs/coredump.c:1049
>  do_coredump fs/coredump.c:1126 [inline]
>  vfs_coredump+0x369e/0x4270 fs/coredump.c:1200
>  get_signal+0x1107/0x1330 kernel/signal.c:3019
>  arch_do_signal_or_restart+0xbc/0x830 arch/x86/kernel/signal.c:337
>  __exit_to_user_mode_loop kernel/entry/common.c:41 [inline]
>  exit_to_user_mode_loop kernel/entry/common.c:75 [inline]
>  __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
>  irqentry_exit_to_user_mode_prepare include/linux/irq-entry-common.h:270 [inline]
>  irqentry_exit_to_user_mode include/linux/irq-entry-common.h:339 [inline]
>  irqentry_exit+0x176/0x620 kernel/entry/common.c:196
>  asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
> RIP: 0033:0x0
> Code: Unable to access opcode bytes at 0xffffffffffffffd6.
> RSP: 002b:0000200000000548 EFLAGS: 00010217
> RAX: 0000000000000000 RBX: 00007efd21615fa0 RCX: 00007efd2139aeb9
> RDX: 0000000000000000 RSI: 0000200000000540 RDI: 0000000000000000
> RBP: 00007efd21408c1f R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007efd21616038 R14: 00007efd21615fa0 R15: 00007ffc2b2553f8
>  </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:ext4_es_cache_extent+0x86e/0x990 fs/ext4/extents_status.c:1043
> Code: e1 07 80 c1 03 38 c1 0f 8c 5d fe ff ff 48 8b 7c 24 20 e8 25 4d af ff e9 4e fe ff ff e8 1b 12 47 ff 90 0f 0b e8 13 12 47 ff 90 <0f> 0b 65 8b 1d 9d 73 6e 10 bf 07 00 00 00 89 de e8 3d 16 47 ff 83
> RSP: 0018:ffffc900054fdba0 EFLAGS: 00010293
> RAX: ffffffff827d2c8d RBX: 0000000000000023 RCX: ffff88801dfe8000
> RDX: 0000000000000000 RSI: 0000000000000030 RDI: 0000000000000023
> RBP: ffffc900054fdce8 R08: ffffc900054fdc57 R09: 0000000000000000
> R10: ffffc900054fdc40 R11: fffff52000a9fb8b R12: 0000000000000030
> R13: dffffc0000000000 R14: 000000000000000f R15: ffff88807d100638
> FS:  00007efd221aa6c0(0000) GS:ffff888125766000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f82eec0f000 CR3: 000000007569c000 CR4: 00000000003526f0

Okay, so this is hitting even before the recent changes. I've made a
logging patch which might help narrow this down.

#syz test: https://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git dev

regards,
ojaswin

> 
> Tested on:
> 
> commit:         26f260ce ext4: remove unnecessary zero-initialization ..
> git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git
> console output: https://syzkaller.appspot.com/x/log.txt?x=12dcd78a580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=a535ad5429f72a2
> dashboard link: https://syzkaller.appspot.com/bug?extid=ccf1421545dbe5caa20c
> compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
> 
> Note: no patches were applied.

View attachment "0001-ext4-add-logging-to-debug-issue.patch" of type "text/plain" (5646 bytes)