diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index cdfa699cd7c8..9d26c5dc4efd 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -1435,6 +1435,11 @@ dbAllocAG(struct bmap * bmp, int agno, s64 nblocks, int l2nb, s64 * results)
 			blkno &= ~(MAXL1SIZE - 1);
 		else		/* bmp->db_aglevel == 0 */
 			blkno &= ~(MAXL0SIZE - 1);
+		
+		if (unlikely(budmin < 0)) {
+   			WARN_ON_ONCE(1);
+    			budmin = 0;
+		}		
 
 		blkno +=
 		    ((s64) (ti - le32_to_cpu(dcp->leafidx))) << budmin;
-- 
2.25.1

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING in dbAllocAG

------------[ cut here ]------------
WARNING: CPU: 1 PID: 6656 at fs/jfs/jfs_dmap.c:1440 dbAllocAG+0xd67/0x1080 fs/jfs/jfs_dmap.c:1440
Modules linked in:
CPU: 1 UID: 0 PID: 6656 Comm: syz.0.22 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
RIP: 0010:dbAllocAG+0xd67/0x1080 fs/jfs/jfs_dmap.c:1440
Code: 89 d8 48 c1 e8 03 42 80 3c 30 00 74 08 48 89 df e8 fe e7 e6 fe 48 8b 3b 48 c7 c6 a0 1a 24 8b e9 d2 f9 ff ff e8 ea 35 85 fe 90 <0f> 0b 90 48 8b 44 24 78 42 0f b6 04 20 84 c0 0f 85 d5 02 00 00 48
RSP: 0018:ffffc90004e4f300 EFLAGS: 00010293
RAX: ffffffff8339c746 RBX: ffff888036d4f000 RCX: ffff88802e0a8000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000100 R11: 0000000000000002 R12: dffffc0000000000
R13: 0000000000000155 R14: 0000000000000000 R15: 00000000000000ff
FS:  00007efe0bfed6c0(0000) GS:ffff888126cc6000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000565151f06950 CR3: 0000000041956000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 dbAlloc+0x5a8/0xba0 fs/jfs/jfs_dmap.c:877
 extBalloc fs/jfs/jfs_extent.c:336 [inline]
 extAlloc+0x54a/0xfb0 fs/jfs/jfs_extent.c:127
 jfs_get_block+0x346/0xab0 fs/jfs/inode.c:254
 __block_write_begin_int+0x6b5/0x1900 fs/buffer.c:2145
 block_write_begin+0x8a/0x120 fs/buffer.c:2256
 jfs_write_begin+0x35/0x80 fs/jfs/inode.c:306
 generic_perform_write+0x29d/0x8c0 mm/filemap.c:4242
 generic_file_write_iter+0x118/0x550 mm/filemap.c:4385
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x5d5/0xb40 fs/read_write.c:686
 ksys_write+0x14b/0x260 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7efe0c99eec9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007efe0bfed038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007efe0cbf6090 RCX: 00007efe0c99eec9
RDX: 0000000000000014 RSI: 0000200000000380 RDI: 0000000000000005
RBP: 00007efe0ca21f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007efe0cbf6128 R14: 00007efe0cbf6090 R15: 00007ffeba24aff8
 </TASK>


Tested on:

commit:         98ac9cc4 Merge tag 'f2fs-fix-6.18-rc2' of git://git.ke..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1606cb04580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=af9170887d81dea1
dashboard link: https://syzkaller.appspot.com/bug?extid=4b717071f1eecb2972df
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=17cfbdcd980000