Re: [PATCH v2 10/27] ftrace: Add subops logic to allow one ops to manage many

Masami Hiramatsu
2024-06-03T02:46:42Z

On Sun, 2 Jun 2024 22:06:13 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> > > +/* Make @ops trace evenything except what all its subops do not trace */
> > > +static struct ftrace_hash *intersect_hashes(struct ftrace_ops *ops)
> > > +{
> > > + struct ftrace_hash *new_hash = NULL;
> > > + struct ftrace_ops *subops;
> > > + int size_bits;
> > > + int ret;
> > > +
> > > + list_for_each_entry(subops, &ops->subop_list, list) {
> > > + struct ftrace_hash *next_hash;
> > > +
> > > + if (!new_hash) {
> > > + size_bits = subops->func_hash->notrace_hash->size_bits;
> > > + new_hash = alloc_and_copy_ftrace_hash(size_bits, ops->func_hash->notrace_hash);
> > > + if (!new_hash)
> > > + return NULL;
> >
> > If the first subops has EMPTY_HASH, this allocates small empty hash (!= EMPTY_HASH)
> > on `new_hash`.
>
> Could we just change the above to be: ?
>
> new_hash = ftrace_hash_empty(ops->func_hash->notrace_hash) ? EMPTY_HASH :
> alloc_and_copy_ftrace_hash(size_bits, ops->func_hash->notrace_hash);
> if (!new_hash)
> return NULL;

Yeah, and if new_hash is EMPTY_HASH, we don't need looping on the rest of
the hashes, right?

>
>
> >
> > > + continue;
> > > + }
> > > + size_bits = new_hash->size_bits;
> > > + next_hash = new_hash;
> >
> > And it is assigned to `next_hash`.
> >
> > > + new_hash = alloc_ftrace_hash(size_bits);
> > > + ret = intersect_hash(&new_hash, next_hash, subops->func_hash->notrace_hash);
> >
> > Since the `next_hash` != EMPTY_HASH but it is empty, this keeps `new_hash`
> > empty but allocated.
> >
> > > + free_ftrace_hash(next_hash);
> > > + if (ret < 0) {
> > > + free_ftrace_hash(new_hash);
> > > + return NULL;
> > > + }
> > > + /* Nothing more to do if new_hash is empty */
> > > + if (new_hash == EMPTY_HASH)
> >
> > Since `new_hash` is empty but != EMPTY_HASH, this does not pass. Keep looping on.
> >
> > > + break;
> > > + }
> > > + return new_hash;
> >
> > And this will return empty but not EMPTY_HASH hash.
> >
> >
> > So, we need;
> >
> > #define FTRACE_EMPTY_HASH_OR_NULL(hash) (!(hash) || (hash) == EMPTY_HASH)
> >
> > if (FTRACE_EMPTY_HASH_OR_NULL(subops->func_hash->notrace_hash)) {
> > free_ftrace_hash(new_hash);
> > new_hash = EMPTY_HASH;
> > break;
> > }
> >
> > at the beginning of the loop.
> > Also, at the end of the loop,
> >
> > if (ftrace_hash_empty(new_hash)) {
> > free_ftrace_hash(new_hash);
> > new_hash = EMPTY_HASH;
> > break;
> > }

And we still need this (I think this should be done in intersect_hash(), we just
need to count the number of entries.)

> >
> > > +}
> > > +
> > > +/* Returns 0 on equal or non-zero on non-equal */
> > > +static int compare_ops(struct ftrace_hash *A, struct ftrace_hash *B)
> >
> > nit: Isn't it better to be `bool hash_equal()` and return true if A == B ?
>
> Sure. I guess I was thinking too much of strcmp() logic :-p

Yeah, it's the curse of the C programmer :( (even it is good for sorting.)

Thank you,

>
> >
> > Thank you,
>
> Thanks for the review.
>
> -- Steve
>
> >
> > > +{
> > > + struct ftrace_func_entry *entry;
> > > + int size;
> > > + int i;
> > > +
> > > + if (!A || A == EMPTY_HASH)
> > > + return !(!B || B == EMPTY_HASH);
> > > +
> > > + if (!B || B == EMPTY_HASH)
> > > + return !(!A || A == EMPTY_HASH);
> > > +
> > > + if (A->count != B->count)
> > > + return 1;
> > > +
> > > + size = 1 << A->size_bits;
> > > + for (i = 0; i < size; i++) {
> > > + hlist_for_each_entry(entry, &A->buckets[i], hlist) {
> > > + if (!__ftrace_lookup_ip(B, entry->ip))
> > > + return 1;
> > > + }
> > > + }
> > > +
> > > + return 0;
> > > +}
> > > +
> >
> >
>

--
Masami Hiramatsu (Google) <mhiramat@kernel.org>