------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: lib/refcount.c:25 at refcount_warn_saturate+0x9f/0x110 lib/refcount.c:25, CPU#1: syz.4.1755/17957
Modules linked in:
CPU: 1 UID: 0 PID: 17957 Comm: syz.4.1755 Tainted: G             L      syzkaller #0 PREEMPT_{RT,(full)} 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:refcount_warn_saturate+0x9f/0x110 lib/refcount.c:25
Code: eb 66 85 db 74 3e 83 fb 01 75 4c e8 4b 3d 01 fd 48 8d 3d e4 d1 f5 0a 67 48 0f b9 3a eb 4a e8 38 3d 01 fd 48 8d 3d e1 d1 f5 0a <67> 48 0f b9 3a eb 37 e8 25 3d 01 fd 48 8d 3d de d1 f5 0a 67 48 0f
RSP: 0018:ffffc900055ffc28 EFLAGS: 00010287
RAX: ffffffff84c44678 RBX: 0000000000000002 RCX: 0000000000080000
RDX: ffffc90010233000 RSI: 000000000000076b RDI: ffffffff8fba1860
RBP: ffffc900055ffd10 R08: ffff8880325b8000 R09: 0000000000000005
R10: 0000000000000100 R11: 0000000000000004 R12: dffffc0000000000
R13: ffff8880749a0eb8 R14: ffff8880749a0eb0 R15: ffff8880749a0e00
FS:  00007f5a374e66c0(0000) GS:ffff888125d3c000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffd424abf52 CR3: 000000003ee96000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __refcount_add include/linux/refcount.h:-1 [inline]
 __refcount_inc include/linux/refcount.h:366 [inline]
 refcount_inc include/linux/refcount.h:383 [inline]
 kref_get include/linux/kref.h:45 [inline]
 dma_fence_get include/linux/dma-fence.h:317 [inline]
 sync_timeline_signal+0x472/0x810 drivers/dma-buf/sw_sync.c:224
 sw_sync_ioctl_inc drivers/dma-buf/sw_sync.c:401 [inline]
 sw_sync_ioctl+0x4f9/0x1110 drivers/dma-buf/sw_sync.c:470
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xff/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x17b/0x530 arch/x86/entry/syscall_64.c:85
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5a3928de99
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:00007f5a374e6028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f5a39515fa0 RCX: 00007f5a3928de99
RDX: 0000200000000280 RSI: 0000000040045701 RDI: 0000000000000003
RBP: 00007f5a39323eaf R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f5a39516038 R14: 00007f5a39515fa0 R15: 00007ffed9ad08c8
 </TASK>
----------------
Code disassembly (best guess):
   0:	eb 66                	jmp    0x68
   2:	85 db                	test   %ebx,%ebx
   4:	74 3e                	je     0x44
   6:	83 fb 01             	cmp    $0x1,%ebx
   9:	75 4c                	jne    0x57
   b:	e8 4b 3d 01 fd       	call   0xfd013d5b
  10:	48 8d 3d e4 d1 f5 0a 	lea    0xaf5d1e4(%rip),%rdi        # 0xaf5d1fb
  17:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  1c:	eb 4a                	jmp    0x68
  1e:	e8 38 3d 01 fd       	call   0xfd013d5b
  23:	48 8d 3d e1 d1 f5 0a 	lea    0xaf5d1e1(%rip),%rdi        # 0xaf5d20b
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	eb 37                	jmp    0x68
  31:	e8 25 3d 01 fd       	call   0xfd013d5b
  36:	48 8d 3d de d1 f5 0a 	lea    0xaf5d1de(%rip),%rdi        # 0xaf5d21b
  3d:	67                   	addr32
  3e:	48                   	rex.W
  3f:	0f                   	.byte 0xf