On Thu, Mar 17, 2022 at 07:25:27AM +0000, Visa Hankala wrote:
> On Thu, Mar 17, 2022 at 12:42:13AM +0100, Alexander Bluhm wrote:
> > I would like to use btrace to debug refernce counting. The idea
> > is to a a tracepoint for every type of refcnt we have. When it
> > changes, print the actual object, the current counter and the change
> > value.
>
> > Do we want that feature?
>
> I am against this in its current form. The code would become more
> complex, and the trace points can affect timing. There is a risk that
> the kernel behaves slightly differently when dt has been compiled in.
Can we get in this part then?
- Remove DIAGNOSTIC to keep similar in non DIAGNOSTIC case.
- Rename refcnt to refs. refcnt is the struct, refs contains the
r_refs value.
- Add KASSERT(refs != ~0) in refcnt_finalize().
- Always use u_int refs so I can insert my btrace diff easily.
Maybe I can optimize btrace diff later.
bluhm
Index: kern/kern_synch.c
===================================================================
RCS file: /data/mirror/openbsd/cvs/src/sys/kern/kern_synch.c,v
retrieving revision 1.184
diff -u -p -r1.184 kern_synch.c
--- kern/kern_synch.c 16 Mar 2022 14:13:01 -0000 1.184
+++ kern/kern_synch.c 17 Mar 2022 16:12:50 -0000
@@ -810,25 +810,21 @@ refcnt_init(struct refcnt *r)
void
refcnt_take(struct refcnt *r)
{
-#ifdef DIAGNOSTIC
- u_int refcnt;
+ u_int refs;
- refcnt = atomic_inc_int_nv(&r->r_refs);
- KASSERT(refcnt != 0);
-#else
- atomic_inc_int(&r->r_refs);
-#endif
+ refs = atomic_inc_int_nv(&r->r_refs);
+ KASSERT(refs != 0);
+ (void)refs;
}
int
refcnt_rele(struct refcnt *r)
{
- u_int refcnt;
+ u_int refs;
- refcnt = atomic_dec_int_nv(&r->r_refs);
- KASSERT(refcnt != ~0);
-
- return (refcnt == 0);
+ refs = atomic_dec_int_nv(&r->r_refs);
+ KASSERT(refs != ~0);
+ return (refs == 0);
}
void
@@ -842,26 +838,33 @@ void
refcnt_finalize(struct refcnt *r, const char *wmesg)
{
struct sleep_state sls;
- u_int refcnt;
+ u_int refs;
- refcnt = atomic_dec_int_nv(&r->r_refs);
- while (refcnt) {
+ refs = atomic_dec_int_nv(&r->r_refs);
+ KASSERT(refs != ~0);
+ while (refs) {
sleep_setup(&sls, r, PWAIT, wmesg, 0);
- refcnt = atomic_load_int(&r->r_refs);
- sleep_finish(&sls, refcnt);
+ refs = atomic_load_int(&r->r_refs);
+ sleep_finish(&sls, refs);
}
}
int
refcnt_shared(struct refcnt *r)
{
- return (atomic_load_int(&r->r_refs) > 1);
+ u_int refs;
+
+ refs = atomic_load_int(&r->r_refs);
+ return (refs > 1);
}
unsigned int
refcnt_read(struct refcnt *r)
{
- return (atomic_load_int(&r->r_refs));
+ u_int refs;
+
+ refs = atomic_load_int(&r->r_refs);
+ return (refs);
}
void
