Reference count race window

[Gumpula, Suresh]

>> Without changing the return-value semantics of refcount_acquire, we 
>> have introduced a panic if we detected a race as below.
>> static __inline void
>> refcount_acquire(volatile u_int *count) {
>>          u_int old;
>>
>>          old = atomic_fetchadd_int(count, 1);
>>          if (old == 0) {
>>            panic("refcount_acquire race condition detected!\n");
>>          }

>>>>>so what is the stacktrace of the panic?

It's from the socket code calling crhold.   It's a non debug build( NO INVARIANTS )

#4  0xffffffff80331d34 in panic (fmt=0xffffffff805c1e60 "refcount_acquire race condition detected!\n") at ../../../../sys/kern/kern_shutdown.c:1009
#5  0xffffffff80326662 in refcount_acquire (count=<optimized out>) at ../../../../sys/sys/refcount.h:65
#6  crhold (cr=<optimized out>) at ../../../../sys/kern/kern_prot.c:1814
#7  0xffffffff803aa0d9 in socreate (dom=<optimized out>, aso=0xffffff80345c1b00, type=<optimized out>, proto=0, cred=0xffffff0017d7aa00, td=0xffffff000b294410) 
at ../../../../sys/kern/uipc_socket.c:441
#8  0xffffffff803b2e5c in socket (td=0xffffff000b294410, uap=0xffffff80345c1be0) at ../../../../sys/kern/uipc_syscalls.c:201
#9  0xffffffff80539ecb in syscall (frame=0xffffff80345c1c80) at ../../../../sys/amd64/amd64/trap.c:1260


Thanks
Suresh