Re: [syzbot] [fs?] [mm?] kernel BUG in __filemap_add_folio

[syzbot <syzbot+4d3cc33ef7a77041efa6@syzkaller.appspotmail.com>]

Hello,

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

 sock_alloc_send_pskb+0x801/0x980 net/core/sock.c:2995
 unix_dgram_sendmsg+0x3c7/0x1820 net/unix/af_unix.c:2127
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg net/socket.c:742 [inline]
 __sys_sendto+0x468/0x4b0 net/socket.c:2206
 __do_sys_sendto net/socket.c:2213 [inline]
 __se_sys_sendto net/socket.c:2209 [inline]
 __x64_sys_sendto+0xe0/0x1c0 net/socket.c:2209
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
------------[ cut here ]------------
kernel BUG at mm/filemap.c:858!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
CPU: 1 UID: 0 PID: 6671 Comm: syz.1.18 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:__filemap_add_folio+0xfcf/0x1280 mm/filemap.c:858
Code: 33 c5 ff 48 c7 c6 e0 16 ba 8b 4c 89 ef e8 e9 3f 12 00 90 0f 0b e8 e1 33 c5 ff 48 c7 c6 40 17 ba 8b 4c 89 ef e8 d2 3f 12 00 90 <0f> 0b e8 ca 33 c5 ff 90 0f 0b 90 e9 4b fe ff ff e8 bc 33 c5 ff 90
RSP: 0018:ffffc900037c7428 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000112cc0 RCX: 0000000000000000
RDX: ffff888031ce24c0 RSI: ffffffff82558dc8 RDI: ffff888031ce2984
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000002
R13: ffffea000142ef40 R14: 0000000000000000 R15: 1ffff920006f8eaf
FS:  00007efde0ba96c0(0000) GS:ffff888124728000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f155571a286 CR3: 000000006b1d7000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 filemap_add_folio+0x1d8/0x690 mm/filemap.c:966
 ra_alloc_folio mm/readahead.c:456 [inline]
 page_cache_ra_order+0x614/0xf30 mm/readahead.c:515
 do_sync_mmap_readahead mm/filemap.c:3405 [inline]
 filemap_fault+0x191a/0x2eb0 mm/filemap.c:3554
 __do_fault+0x10d/0x550 mm/memory.c:5364
 do_shared_fault mm/memory.c:5863 [inline]
 do_fault+0x2db/0x1990 mm/memory.c:5937
 do_pte_missing mm/memory.c:4477 [inline]
 handle_pte_fault mm/memory.c:6317 [inline]
 __handle_mm_fault+0x180f/0x2b60 mm/memory.c:6455
 handle_mm_fault+0x36d/0xa20 mm/memory.c:6624
 faultin_page mm/gup.c:1126 [inline]
 __get_user_pages+0xf9c/0x34d0 mm/gup.c:1428
 __get_user_pages_locked mm/gup.c:1692 [inline]
 faultin_page_range+0x1f1/0x9e0 mm/gup.c:1912
 madvise_populate mm/madvise.c:974 [inline]
 madvise_do_behavior+0x354/0x510 mm/madvise.c:1933
 do_madvise+0x195/0x240 mm/madvise.c:2028
 __do_sys_madvise mm/madvise.c:2037 [inline]
 __se_sys_madvise mm/madvise.c:2035 [inline]
 __x64_sys_madvise+0xa9/0x110 mm/madvise.c:2035
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7efddfd9aef9
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:00007efde0ba9028 EFLAGS: 00000246 ORIG_RAX: 000000000000001c
RAX: ffffffffffffffda RBX: 00007efde0005fa0 RCX: 00007efddfd9aef9
RDX: 0000000000000017 RSI: 0000000000c00000 RDI: 0000200000000000
RBP: 00007efddfe2fee0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007efde0006038 R14: 00007efde0005fa0 R15: 00007ffccbb43488
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:__filemap_add_folio+0xfcf/0x1280 mm/filemap.c:858
Code: 33 c5 ff 48 c7 c6 e0 16 ba 8b 4c 89 ef e8 e9 3f 12 00 90 0f 0b e8 e1 33 c5 ff 48 c7 c6 40 17 ba 8b 4c 89 ef e8 d2 3f 12 00 90 <0f> 0b e8 ca 33 c5 ff 90 0f 0b 90 e9 4b fe ff ff e8 bc 33 c5 ff 90
RSP: 0018:ffffc900037c7428 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000112cc0 RCX: 0000000000000000
RDX: ffff888031ce24c0 RSI: ffffffff82558dc8 RDI: ffff888031ce2984
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000002
R13: ffffea000142ef40 R14: 0000000000000000 R15: 1ffff920006f8eaf
FS:  00007efde0ba96c0(0000) GS:ffff888124628000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f577493d9e8 CR3: 000000006b1d7000 CR4: 00000000003526f0


Tested on:

commit:         e3c33bc7 Merge tag 'mm-hotfixes-stable-2026-03-23-17-5..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13e4d6da580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=75b16ce1bc745e05
dashboard link: https://syzkaller.appspot.com/bug?extid=4d3cc33ef7a77041efa6
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

Note: no patches were applied.