syzbot

9p: Unknown Cache mode or invalid value fs
9pnet: Tag 65535 still in use
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 2 PID: 6261 at lib/refcount.c:28 refcount_warn_saturate+0x14a/0x210 lib/refcount.c:28
Modules linked in:
CPU: 2 UID: 0 PID: 6261 Comm: syz.2.58 Not tainted 6.15.0-rc1-syzkaller-00246-g900241a5cc15 #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:refcount_warn_saturate+0x14a/0x210 lib/refcount.c:28
Code: ff 89 de e8 08 ab eb fc 84 db 0f 85 66 ff ff ff e8 1b b0 eb fc c6 05 5e 26 9f 0b 01 90 48 c7 c7 40 0f f4 8b e8 f7 40 ab fc 90 <0f> 0b 90 90 e9 43 ff ff ff e8 f8 af eb fc 0f b6 1d 39 26 9f 0b 31
RSP: 0018:ffffc900033479e0 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff817acff8
RDX: ffff88802d434880 RSI: ffffffff817ad005 RDI: 0000000000000001
RBP: ffff88802814aaa8 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffff88802814aaa8
R13: ffff88802ef29000 R14: dffffc0000000000 R15: 1ffff92000668f47
FS:  00007f53b8b516c0(0000) GS:ffff8880d6bb3000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000001000 CR3: 0000000036166000 CR4: 0000000000352ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 __refcount_sub_and_test include/linux/refcount.h:400 [inline]
 __refcount_dec_and_test include/linux/refcount.h:432 [inline]
 refcount_dec_and_test include/linux/refcount.h:450 [inline]
 p9_req_put+0x1ec/0x250 net/9p/client.c:404
 p9_tag_cleanup net/9p/client.c:431 [inline]
 p9_client_destroy+0x22b/0x480 net/9p/client.c:1086
 v9fs_session_init+0xbab/0x1a80 fs/9p/v9fs.c:490
 v9fs_mount+0xc5/0xa30 fs/9p/vfs_super.c:122
 legacy_get_tree+0x109/0x220 fs/fs_context.c:662
 vfs_get_tree+0x8b/0x340 fs/super.c:1759
 do_new_mount fs/namespace.c:3879 [inline]
 path_mount+0x14d4/0x1f30 fs/namespace.c:4206
 do_mount fs/namespace.c:4219 [inline]
 __do_sys_mount fs/namespace.c:4430 [inline]
 __se_sys_mount fs/namespace.c:4407 [inline]
 __x64_sys_mount+0x28d/0x310 fs/namespace.c:4407
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x260 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f53b7d8d169
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:00007f53b8b51038 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f53b7fa5fa0 RCX: 00007f53b7d8d169
RDX: 00002000000004c0 RSI: 0000200000000480 RDI: 00002000000001c0
RBP: 00007f53b7e0e990 R08: 0000200000000840 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f53b7fa5fa0 R15: 00007ffc0d133e78
 </TASK>