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

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Message-ID: <698b4d93.a70a0220.2c38d7.0075.GAE@google.com>
Date: Tue, 10 Feb 2026 07:24:03 -0800
From: syzbot <syzbot+ccf1421545dbe5caa20c@...kaller.appspotmail.com>
To: adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org, 
	linux-kernel@...r.kernel.org, ojaswin@...ux.ibm.com, 
	syzkaller-bugs@...glegroups.com, tytso@....edu
Subject: Re: [syzbot] [ext4?] kernel BUG in ext4_es_cache_extent (4)

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
kernel BUG in ext4_ext_insert_extent

inode 15: block 305:freeing already freed block (bit 19); block bitmap corrupt.
------------[ cut here ]------------
kernel BUG at fs/ext4/extents.c:2174!
Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
CPU: 0 UID: 0 PID: 6747 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
RIP: 0010:ext4_ext_insert_extent+0x5248/0x5280 fs/ext4/extents.c:2174
Code: 89 d9 80 e1 07 fe c1 38 c1 0f 8c 75 e4 ff ff 48 89 df e8 1b 8f b1 ff e9 68 e4 ff ff e8 41 54 49 ff 90 0f 0b e8 39 54 49 ff 90 <0f> 0b e8 31 54 49 ff 90 0f 0b 89 d9 80 e1 07 80 c1 03 38 c1 0f 8c
RSP: 0018:ffffc9000426ebe0 EFLAGS: 00010293
RAX: ffffffff827aea67 RBX: 0000000000000021 RCX: ffff88802fe9db80
RDX: 0000000000000000 RSI: 0000000000000021 RDI: 0000000000000021
RBP: ffffc9000426edd0 R08: ffff888076d2d0ef R09: 1ffff1100eda5a1d
R10: dffffc0000000000 R11: ffffed100eda5a1e R12: ffff888063f4b43c
R13: ffff888143ff8500 R14: ffff888063f4b400 R15: 0000000000000021
FS:  00007efc4003a6c0(0000) GS:ffff888125766000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000003000 CR3: 0000000028bcc000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 ext4_ext_map_blocks+0x168a/0x5760 fs/ext4/extents.c:4480
 ext4_map_create_blocks+0x11d/0x540 fs/ext4/inode.c:616
 ext4_map_blocks+0x7cd/0x11d0 fs/ext4/inode.c:809
 _ext4_get_block+0x1e3/0x470 fs/ext4/inode.c:909
 ext4_get_block_unwritten+0x2e/0x100 fs/ext4/inode.c:942
 ext4_block_write_begin+0xb14/0x1950 fs/ext4/inode.c:1196
 ext4_write_begin+0xb40/0x1870 fs/ext4/ext4_jbd2.h:-1
 ext4_da_write_begin+0x355/0xd30 fs/ext4/inode.c:3123
 generic_perform_write+0x2e2/0x8f0 mm/filemap.c:4314
 ext4_buffered_write_iter+0xce/0x3a0 fs/ext4/file.c:299
 ext4_file_write_iter+0x298/0x1bf0 fs/ext4/file.c:-1
 do_iter_readv_writev+0x619/0x8c0 fs/read_write.c:-1
 vfs_writev+0x33c/0x990 fs/read_write.c:1057
 do_pwritev fs/read_write.c:1153 [inline]
 __do_sys_pwritev2 fs/read_write.c:1211 [inline]
 __se_sys_pwritev2+0x184/0x2a0 fs/read_write.c:1202
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7efc3f19aeb9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007efc4003a028 EFLAGS: 00000246 ORIG_RAX: 0000000000000148
RAX: ffffffffffffffda RBX: 00007efc3f415fa0 RCX: 00007efc3f19aeb9
RDX: 0000000000000001 RSI: 0000200000000100 RDI: 0000000000000004
RBP: 00007efc3f208c1f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000005412 R11: 0000000000000246 R12: 0000000000000000
R13: 00007efc3f416038 R14: 00007efc3f415fa0 R15: 00007ffefdbddaa8
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:ext4_ext_insert_extent+0x5248/0x5280 fs/ext4/extents.c:2174
Code: 89 d9 80 e1 07 fe c1 38 c1 0f 8c 75 e4 ff ff 48 89 df e8 1b 8f b1 ff e9 68 e4 ff ff e8 41 54 49 ff 90 0f 0b e8 39 54 49 ff 90 <0f> 0b e8 31 54 49 ff 90 0f 0b 89 d9 80 e1 07 80 c1 03 38 c1 0f 8c
RSP: 0018:ffffc9000426ebe0 EFLAGS: 00010293
RAX: ffffffff827aea67 RBX: 0000000000000021 RCX: ffff88802fe9db80
RDX: 0000000000000000 RSI: 0000000000000021 RDI: 0000000000000021
RBP: ffffc9000426edd0 R08: ffff888076d2d0ef R09: 1ffff1100eda5a1d
R10: dffffc0000000000 R11: ffffed100eda5a1e R12: ffff888063f4b43c
R13: ffff888143ff8500 R14: ffff888063f4b400 R15: 0000000000000021
FS:  00007efc4003a6c0(0000) GS:ffff888125866000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fc4a9f45000 CR3: 0000000028bcc000 CR4: 00000000003526f0


Tested on:

commit:         4f5e8e6f et4: allow zeroout when doing written to unwr..
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git dev
console output: https://syzkaller.appspot.com/x/log.txt?x=1081d33a580000
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
patch:          https://syzkaller.appspot.com/x/patch.diff?x=10c15194580000