Re: [syzbot] [ext4?] kernel BUG in ext4_es_cache_extent (4)

[syzbot <syzbot+ccf1421545dbe5caa20c@syzkaller.appspotmail.com>]

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 loop0): ext4_mb_new_blocks:6274: inode #15: comm syz.0.55: ext4_mb_new_blocks: Allocation requested for: lblk:0 len:1
EXT4-fs warning (device loop0): ext4_mb_regular_allocator:3120: inode #15: comm syz.0.55: ext4_mb_regular_allocator: Best len 1, origin len 1, ac_status 2, ac_flags 0xa0, cr 5 ret 0
------------[ cut here ]------------
kernel BUG at fs/ext4/extents_status.c:1057!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
CPU: 1 UID: 0 PID: 6693 Comm: syz.0.55 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/27/2026
RIP: 0010:ext4_es_cache_extent+0x8eb/0xa10 fs/ext4/extents_status.c:1057
Code: e1 07 80 c1 03 38 c1 0f 8c 51 fe ff ff 48 8b 7c 24 18 e8 f8 54 af ff e9 42 fe ff ff e8 ee 19 47 ff 90 0f 0b e8 e6 19 47 ff 90 <0f> 0b 65 8b 1d 70 7b 6e 10 bf 07 00 00 00 89 de e8 10 1e 47 ff 83
RSP: 0018:ffffc900041aec20 EFLAGS: 00010293
RAX: ffffffff827d24ba RBX: 0000000000000060 RCX: ffff88802d9f3d00
RDX: 0000000000000000 RSI: 0000000000000064 RDI: 0000000000000060
RBP: ffffc900041aed80 R08: ffff88807eaeca47 R09: 1ffff1100fd5d948
R10: dffffc0000000000 R11: ffffed100fd5d949 R12: 0000000000000008
R13: dffffc0000000000 R14: 000000000000000f R15: 0000000000000064
FS:  00007fca40bd36c0(0000) GS:ffff888125866000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000011000 CR3: 000000007715a000 CR4: 0000000000350ef0
Call Trace:
 <TASK>
 ext4_cache_extents+0x143/0x2f0 fs/ext4/extents.c:540
 __read_extent_tree_block+0x3b8/0x580 fs/ext4/extents.c:587
 ext4_find_extent+0x5bb/0xa20 fs/ext4/extents.c:942
 ext4_ext_map_blocks+0x27a/0x5730 fs/ext4/extents.c:4285
 ext4_map_query_blocks+0x13b/0xa00 fs/ext4/inode.c:553
 ext4_map_blocks+0x444/0x11d0 fs/ext4/inode.c:771
 _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
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x61d/0xb90 fs/read_write.c:686
 ksys_pwrite64 fs/read_write.c:793 [inline]
 __do_sys_pwrite64 fs/read_write.c:801 [inline]
 __se_sys_pwrite64 fs/read_write.c:798 [inline]
 __x64_sys_pwrite64+0x199/0x230 fs/read_write.c:798
 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: 0033:0x7fca3fd9c799
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:00007fca40bd3028 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
RAX: ffffffffffffffda RBX: 00007fca40016090 RCX: 00007fca3fd9c799
RDX: 00000000200000c1 RSI: 00002000000000c0 RDI: 0000000000000006
RBP: 00007fca3fe32bd9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000009000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fca40016128 R14: 00007fca40016090 R15: 00007ffe8193e178
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:ext4_es_cache_extent+0x8eb/0xa10 fs/ext4/extents_status.c:1057
Code: e1 07 80 c1 03 38 c1 0f 8c 51 fe ff ff 48 8b 7c 24 18 e8 f8 54 af ff e9 42 fe ff ff e8 ee 19 47 ff 90 0f 0b e8 e6 19 47 ff 90 <0f> 0b 65 8b 1d 70 7b 6e 10 bf 07 00 00 00 89 de e8 10 1e 47 ff 83
RSP: 0018:ffffc900041aec20 EFLAGS: 00010293
RAX: ffffffff827d24ba RBX: 0000000000000060 RCX: ffff88802d9f3d00
RDX: 0000000000000000 RSI: 0000000000000064 RDI: 0000000000000060
RBP: ffffc900041aed80 R08: ffff88807eaeca47 R09: 1ffff1100fd5d948
R10: dffffc0000000000 R11: ffffed100fd5d949 R12: 0000000000000008
R13: dffffc0000000000 R14: 000000000000000f R15: 0000000000000064
FS:  00007fca40bd36c0(0000) GS:ffff888125866000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000011000 CR3: 000000007715a000 CR4: 0000000000350ef0


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=1236cd52580000
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=1696cd52580000