linux-ext4 - Re: [syzbot] [ext4?] kernel BUG in ext4_ext_insert

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Message-ID: <6871845d.a00a0220.26a83e.005f.GAE@google.com>
Date: Fri, 11 Jul 2025 14:38:37 -0700
From: syzbot <syzbot+ad86dcdffd6785f56e03@...kaller.appspotmail.com>
To: adilger.kernel@...ger.ca, akpm@...ux-foundation.org, 
	dave.hansen@...ux.intel.com, linux-ext4@...r.kernel.org, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, syzkaller-bugs@...glegroups.com, tytso@....edu, 
	willy@...radead.org
Subject: Re: [syzbot] [ext4?] kernel BUG in ext4_ext_insert_extent (2)

syzbot has found a reproducer for the following issue on:

HEAD commit:    40f92e79b0aa Merge tag 'block-6.16-20250710' of git://git...
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=14314d82580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=bd2783a0a99d4ed0
dashboard link: https://syzkaller.appspot.com/bug?extid=ad86dcdffd6785f56e03
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11ce7a8c580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=152fc68c580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f33b9048bb66/disk-40f92e79.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1194a16e19e9/vmlinux-40f92e79.xz
kernel image: https://storage.googleapis.com/syzbot-assets/bd82e554bd44/bzImage-40f92e79.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/ead6dd3b0e30/mount_0.gz
  fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=17a760f0580000)

The issue was bisected to:

commit 665575cff098b696995ddaddf4646a4099941f5e
Author: Dave Hansen <dave.hansen@...ux.intel.com>
Date:   Fri Feb 28 20:37:22 2025 +0000

    filemap: move prefaulting out of hot write path

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1434a3d4580000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=1634a3d4580000
console output: https://syzkaller.appspot.com/x/log.txt?x=1234a3d4580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ad86dcdffd6785f56e03@...kaller.appspotmail.com
Fixes: 665575cff098 ("filemap: move prefaulting out of hot write path")

------------[ cut here ]------------
kernel BUG at fs/ext4/extents.c:2153!
Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
CPU: 1 UID: 0 PID: 5856 Comm: syz-executor355 Not tainted 6.16.0-rc5-syzkaller-00193-g40f92e79b0aa #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:ext4_ext_insert_extent+0x4ab7/0x4af0 fs/ext4/extents.c:2153
Code: 89 d9 80 e1 07 fe c1 38 c1 0f 8c a6 e7 ff ff 48 89 df e8 3c 95 b6 ff e9 99 e7 ff ff e8 a2 3d 55 ff 90 0f 0b e8 9a 3d 55 ff 90 <0f> 0b e8 92 3d 55 ff 90 0f 0b 89 d9 80 e1 07 80 c1 03 38 c1 0f 8c
RSP: 0018:ffffc9000437ec60 EFLAGS: 00010293
RAX: ffffffff826af7b6 RBX: 000000000000001d RCX: ffff88802dd18000
RDX: 0000000000000000 RSI: 000000000000001d RDI: 000000000000001d
RBP: ffffc9000437ee10 R08: ffff8880738b3ae7 R09: 1ffff1100e71675c
R10: dffffc0000000000 R11: ffffed100e71675d R12: 000000000000001d
R13: dffffc0000000000 R14: ffff8880721f643c R15: ffff888027204700
FS:  00007fa4a23966c0(0000) GS:ffff888125d4f000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f42dc5c1000 CR3: 000000003299c000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 ext4_ext_map_blocks+0x1792/0x6ac0 fs/ext4/extents.c:4404
 ext4_map_create_blocks fs/ext4/inode.c:609 [inline]
 ext4_map_blocks+0x931/0x18d0 fs/ext4/inode.c:813
 _ext4_get_block+0x200/0x4c0 fs/ext4/inode.c:892
 ext4_get_block_unwritten+0x2e/0x100 fs/ext4/inode.c:925
 ext4_block_write_begin+0x6f8/0x14b0 fs/ext4/inode.c:1178
 ext4_write_begin+0xa4f/0x1680 fs/ext4/ext4_jbd2.h:-1
 ext4_da_write_begin+0x449/0xd20 fs/ext4/inode.c:3057
 generic_perform_write+0x2c4/0x910 mm/filemap.c:4112
 ext4_buffered_write_iter+0xce/0x3a0 fs/ext4/file.c:299
 ext4_dio_write_iter fs/ext4/file.c:613 [inline]
 ext4_file_write_iter+0x182a/0x1bc0 fs/ext4/file.c:721
 do_iter_readv_writev+0x56b/0x7f0 fs/read_write.c:-1
 vfs_writev+0x31a/0x960 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+0x179/0x290 fs/read_write.c:1202
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa4a23e16f9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 81 18 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fa4a2396208 EFLAGS: 00000246 ORIG_RAX: 0000000000000148
RAX: ffffffffffffffda RBX: 00007fa4a2468648 RCX: 00007fa4a23e16f9
RDX: 0000000000000001 RSI: 00002000000001c0 RDI: 0000000000000007
RBP: 00007fa4a2468640 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000e7b R11: 0000000000000246 R12: 00007fa4a2435620
R13: 0000200000000140 R14: 00002000000001c0 R15: 0000200000000080
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:ext4_ext_insert_extent+0x4ab7/0x4af0 fs/ext4/extents.c:2153
Code: 89 d9 80 e1 07 fe c1 38 c1 0f 8c a6 e7 ff ff 48 89 df e8 3c 95 b6 ff e9 99 e7 ff ff e8 a2 3d 55 ff 90 0f 0b e8 9a 3d 55 ff 90 <0f> 0b e8 92 3d 55 ff 90 0f 0b 89 d9 80 e1 07 80 c1 03 38 c1 0f 8c
RSP: 0018:ffffc9000437ec60 EFLAGS: 00010293

RAX: ffffffff826af7b6 RBX: 000000000000001d RCX: ffff88802dd18000
RDX: 0000000000000000 RSI: 000000000000001d RDI: 000000000000001d
RBP: ffffc9000437ee10 R08: ffff8880738b3ae7 R09: 1ffff1100e71675c
R10: dffffc0000000000 R11: ffffed100e71675d R12: 000000000000001d
R13: dffffc0000000000 R14: ffff8880721f643c R15: ffff888027204700
FS:  00007fa4a23966c0(0000) GS:ffff888125d4f000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fff12275000 CR3: 000000003299c000 CR4: 00000000003526f0


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.