------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: lib/refcount.c:28 at refcount_warn_saturate+0xf4/0x130 lib/refcount.c:28, CPU#0: syz.2.864/9155
Modules linked in:
CPU: 0 UID: 0 PID: 9155 Comm: syz.2.864 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:refcount_warn_saturate+0xf4/0x130 lib/refcount.c:28
Code: cc e8 60 d1 0f fd 48 8d 3d 89 0c eb 0b 67 48 0f b9 3a e8 4f d1 0f fd 5b 5d e9 88 81 94 06 e8 43 d1 0f fd 48 8d 3d 7c 0c eb 0b <67> 48 0f b9 3a e8 32 d1 0f fd 5b 5d c3 cc cc cc cc e8 26 d1 0f fd
RSP: 0018:ffffc90000007d98 EFLAGS: 00010046
RAX: 0000000080010002 RBX: ffff88804b228dd8 RCX: ffffffff84f8cf0b
RDX: ffff888023262540 RSI: ffffffff84f8cf9d RDI: ffffffff90e3dc20
RBP: 0000000000000003 R08: 0000000000000005 R09: 0000000000000004
R10: 0000000000000003 R11: 000000000000001e R12: ffff88804b228dd8
R13: ffff8880790f8c00 R14: 000000000000000b R15: 1ffff1100415380c
FS:  0000000000000000(0000) GS:ffff888097166000(0063) knlGS:00000000f5475b40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 00000000f741157c CR3: 0000000078924000 CR4: 0000000000352ef0
Call Trace:
 <IRQ>
 __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:281
 req_done+0x1dc/0x2e0 net/9p/trans_virtio.c:147
 vring_interrupt+0x2ef/0x650 drivers/virtio/virtio_ring.c:3254
 __handle_irq_event_percpu+0x232/0x880 kernel/irq/handle.c:209
 handle_irq_event_percpu kernel/irq/handle.c:246 [inline]
 handle_irq_event+0xab/0x1e0 kernel/irq/handle.c:263
 handle_edge_irq+0x34c/0x950 kernel/irq/chip.c:859
 generic_handle_irq_desc include/linux/irqdesc.h:188 [inline]
 handle_irq arch/x86/kernel/irq.c:209 [inline]
 call_irq_handler arch/x86/kernel/irq.c:265 [inline]
 __common_interrupt+0xd8/0x2f0 arch/x86/kernel/irq.c:280
 common_interrupt+0xb9/0xe0 arch/x86/kernel/irq.c:273
 </IRQ>
 <TASK>
 asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:665
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:179 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0x31/0x80 kernel/locking/spinlock.c:198
Code: f5 53 48 8b 74 24 10 48 89 fb 48 83 c7 18 e8 c6 5f 57 f6 48 89 df e8 4e af 57 f6 f7 c5 00 02 00 00 75 23 9c 58 f6 c4 02 75 37 <bf> 01 00 00 00 e8 75 bd 46 f6 65 8b 05 1e 99 7e 08 85 c0 74 16 5b
RSP: 0018:ffffc900032b7808 EFLAGS: 00000246

RAX: 0000000000000046 RBX: ffff8880252e8f80 RCX: ffffffff8210e1df
RDX: 0000000000000000 RSI: ffffffff8c1ce280 RDI: ffffffff8b8d0722
RBP: 0000000000000282 R08: 0000000000000000 R09: fffffbfff21b2432
R10: 0000000000000000 R11: 0000000000000001 R12: ffff8880252e8e10
R13: ffff8880252e8fc0 R14: ffff8880252e8968 R15: ffff8880259bc280
 __unix_dgram_recvmsg+0x31a/0xc30 net/unix/af_unix.c:2612
 unix_dgram_recvmsg+0xcd/0x100 net/unix/af_unix.c:2686
 sock_recvmsg_nosec net/socket.c:1126 [inline]
 ____sys_recvmsg+0x5b3/0x640 net/socket.c:2902
 ___sys_recvmsg+0x16a/0x1a0 net/socket.c:2946
 do_recvmmsg+0x54d/0x740 net/socket.c:3033
 __sys_recvmmsg+0x21f/0x270 net/socket.c:3115
 __do_compat_sys_recvmmsg_time32 net/compat.c:417 [inline]
 __se_compat_sys_recvmmsg_time32 net/compat.c:413 [inline]
 __ia32_compat_sys_recvmmsg_time32+0xc4/0x160 net/compat.c:413
 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
 __do_fast_syscall_32+0xe7/0x970 arch/x86/entry/syscall_32.c:307
 do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:332
 entry_SYSENTER_compat_after_hwframe+0x84/0x8e
RIP: 0023:0xf7fd4fec
Code: Unable to access opcode bytes at 0xf7fd4fc2.
RSP: 002b:00000000f547550c EFLAGS: 00000292 ORIG_RAX: 0000000000000151
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 0000000080000040
RDX: 00000000080002c1 RSI: 0000000000000002 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000292 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>
----------------
Code disassembly (best guess):
   0:	cc                   	int3
   1:	e8 60 d1 0f fd       	call   0xfd0fd166
   6:	48 8d 3d 89 0c eb 0b 	lea    0xbeb0c89(%rip),%rdi        # 0xbeb0c96
   d:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  12:	e8 4f d1 0f fd       	call   0xfd0fd166
  17:	5b                   	pop    %rbx
  18:	5d                   	pop    %rbp
  19:	e9 88 81 94 06       	jmp    0x69481a6
  1e:	e8 43 d1 0f fd       	call   0xfd0fd166
  23:	48 8d 3d 7c 0c eb 0b 	lea    0xbeb0c7c(%rip),%rdi        # 0xbeb0ca6
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	e8 32 d1 0f fd       	call   0xfd0fd166
  34:	5b                   	pop    %rbx
  35:	5d                   	pop    %rbp
  36:	c3                   	ret
  37:	cc                   	int3
  38:	cc                   	int3
  39:	cc                   	int3
  3a:	cc                   	int3
  3b:	e8 26 d1 0f fd       	call   0xfd0fd166