Re: [syzbot] [v9fs?] WARNING in v9fs_init_request (2)

[syzbot <syzbot+344c09c64fcd8d3d2782@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING in v9fs_init_request

DIAG: single-component p9_client_walk failed, name=file0 err=-2
------------[ cut here ]------------
DIAG: v9fs_init_request: v9fs_fid_lookup failed for symlink, err=-2 dentry=/file0 inode->i_ino=2e41983
WARNING: fs/9p/vfs_addr.c:155 at v9fs_init_request+0x4ac/0x690 fs/9p/vfs_addr.c:155, CPU#3: syz.0.19/6266
Modules linked in:
CPU: 3 UID: 0 PID: 6266 Comm: syz.0.19 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:v9fs_init_request+0x4b6/0x690 fs/9p/vfs_addr.c:155
Code: 00 fc ff df 48 8d 7d 40 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 c6 01 00 00 48 8d 3d 74 a5 20 0d 48 8b 4d 40 4c 89 e2 48 89 de <67> 48 0f b9 3a 4c 89 e7 e8 0d b6 8b fe e9 dc fd ff ff e8 a3 83 ff
RSP: 0018:ffffc90003877778 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: fffffffffffffffe RCX: 0000000002e41983
RDX: ffff8880396a7028 RSI: fffffffffffffffe RDI: ffffffff912afe50
RBP: ffff88804672f580 R08: 0000000000000007 R09: fffffffffffff000
R10: fffffffffffffffe R11: 0000000000000000 R12: ffff8880396a7028
R13: ffff888026eb8e41 R14: ffff888026eb8bd0 R15: ffff88804672f580
FS:  00007f377f3f26c0(0000) GS:ffff8880d60e3000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000002784b000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 netfs_alloc_request+0x71c/0xcb0 fs/netfs/objects.c:72
 netfs_read_folio+0x20c/0x13f0 fs/netfs/buffered_read.c:513
 filemap_read_folio+0xfc/0x3b0 mm/filemap.c:2510
 do_read_cache_folio+0x2d7/0x6b0 mm/filemap.c:4140
 read_mapping_folio include/linux/pagemap.h:1015 [inline]
 __page_get_link.isra.0+0x30/0x350 fs/namei.c:6336
 page_get_link+0x44/0xf0 fs/namei.c:6366
 v9fs_vfs_get_link_dotl+0x27b/0x310 fs/9p/vfs_inode_dotl.c:930
 pick_link+0xd17/0x13c0 fs/namei.c:2068
 step_into_slowpath+0x9ba/0xf90 fs/namei.c:2127
 step_into fs/namei.c:2152 [inline]
 walk_component fs/namei.c:2288 [inline]
 lookup_last fs/namei.c:2789 [inline]
 path_lookupat+0x58b/0xc40 fs/namei.c:2813
 filename_lookup+0x202/0x590 fs/namei.c:2842
 user_path_at+0x3c/0x60 fs/namei.c:3641
 do_mount fs/namespace.c:4171 [inline]
 __do_sys_mount fs/namespace.c:4390 [inline]
 __se_sys_mount fs/namespace.c:4367 [inline]
 __x64_sys_mount+0x1fb/0x310 fs/namespace.c:4367
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f377e59de99
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:00007f377f3f2028 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f377e825fa0 RCX: 00007f377e59de99
RDX: 00002000000004c0 RSI: 0000200000000480 RDI: 0000000000000000
RBP: 00007f377e633eaf R08: 0000200000000c00 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f377e826038 R14: 00007f377e825fa0 R15: 00007fff970da688
 </TASK>
----------------
Code disassembly (best guess):
   0:	00 fc                	add    %bh,%ah
   2:	ff                   	lcall  (bad)
   3:	df 48 8d             	fisttps -0x73(%rax)
   6:	7d 40                	jge    0x48
   8:	48 89 fa             	mov    %rdi,%rdx
   b:	48 c1 ea 03          	shr    $0x3,%rdx
   f:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1)
  13:	0f 85 c6 01 00 00    	jne    0x1df
  19:	48 8d 3d 74 a5 20 0d 	lea    0xd20a574(%rip),%rdi        # 0xd20a594
  20:	48 8b 4d 40          	mov    0x40(%rbp),%rcx
  24:	4c 89 e2             	mov    %r12,%rdx
  27:	48 89 de             	mov    %rbx,%rsi
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	4c 89 e7             	mov    %r12,%rdi
  32:	e8 0d b6 8b fe       	call   0xfe8bb644
  37:	e9 dc fd ff ff       	jmp    0xfffffe18
  3c:	e8                   	.byte 0xe8
  3d:	a3                   	.byte 0xa3
  3e:	83                   	.byte 0x83
  3f:	ff                   	.byte 0xff


Tested on:

commit:         e2a93699 Merge tag 'drm-fixes-2026-07-25' of https://g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=107a5fde580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d69870d5e052935f
dashboard link: https://syzkaller.appspot.com/bug?extid=344c09c64fcd8d3d2782
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
patch:          https://syzkaller.appspot.com/x/patch.diff?x=1348dca9580000