On Thu, Aug 14, 2025 at 12:15:04PM +0900, Masami Hiramatsu wrote:
> Hi Ryan,
>
> On Wed, 13 Aug 2025 01:21:01 +0900
> Ryan Chung <seokwoo.chung...@gmail.com> wrote:
>
> > Resolve TODO in `__register_trace_fprobe()`:
> > parse `tf->symbol` robustly (support `sym!filter` and comma-separated
> > lists), trim tokens, ignore empties, deduplicate symbols, use bulk
> > registration for lists, return `-EEXIST` if already registered, and
> > preserve lockdown/tracepoint deferral semantics.
>
> Thanks for the improvement!
> And could you add the new syntax in the document too ?
>
Yes. I will add the syntax in the document.
To clarify, by document, you mean
Documentation/trace/fprobetrace.rst?
> >
> > Please note that this was my personal interpretation of what TODO
> > required here. Welcoming any feedback.
> >
> > Signed-off-by: Ryan Chung <seokwoo.chung...@gmail.com>
> > ---
> > kernel/trace/trace_fprobe.c | 102 +++++++++++++++++++++++++++++++++++-
> > 1 file changed, 100 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/trace/trace_fprobe.c b/kernel/trace/trace_fprobe.c
> > index b40fa59159ac..37d4260b9012 100644
> > --- a/kernel/trace/trace_fprobe.c
> > +++ b/kernel/trace/trace_fprobe.c
> > @@ -12,6 +12,8 @@
> > #include <linux/security.h>
> > #include <linux/tracepoint.h>
> > #include <linux/uaccess.h>
> > +#include <linux/string.h>
> > +#include <linux/slab.h>
>
> Headers should be sorted alphabetically.
>
I will fix this in v2.
> >
> > #include "trace_dynevent.h"
> > #include "trace_probe.h"
> > @@ -762,8 +764,104 @@ static int __register_trace_fprobe(struct
> > trace_fprobe *tf)
> > return __regsiter_tracepoint_fprobe(tf);
> > }
> >
> > - /* TODO: handle filter, nofilter or symbol list */
> > - return register_fprobe(&tf->fp, tf->symbol, NULL);
> > + /* Parse tf->symbol */
>
> Please make this parse and check as a sub-function instead of new
> scope. Also, it should be done in parse_symbol_and_return(), so that
> we can handle wrong syntax when parsing it.
>
I will move the parsing into parse_symbol_and_return()
so syntax errors are detected at parse time.
> > + {
> > + char *spec, *bang, *p;
> > + int n = 0, w = 0, j, rc;
> > + char **syms = NULL;
> > +
> > + spec = kstrdup(tf->symbol, GFP_KERNEL);
> > + if (!spec)
> > + return -ENOMEM;
> > +
> > + /* If a '!' exists, treat it as single symbol + filter */
> > + bang = strchr(spec, '!');
> > + if (bang) {
> > + char *sym, *flt;
> > +
> > + *bang = '\0';
> > + sym = strim(spec);
> > + flt = strim(bang + 1);
>
> You don't need to do strim, since if there is a space, it
> should be parsed already. New syntax must be ',' separated.
> My basic syntax for this probe event is;
>
> WORD WORD WORD[:OPTWORD] SUBWORD[,SUBWORD]
>
> OPTWORD is qualifying the previous WORD, SUBWORDs are not
> quarifying, but the same-level words. (Currently using "%return"
> for the return of the function, that is a special case.)
>
Understood. I will drop strim() and treat tokens as you mentioned.
I will leave return behavior unchanged.
> > +
> > + if (!*sym || !*flt) {
> > + kfree(spec);
>
> Please use __free(kfree) instead of repeating kfree().
>
I will also include this in v2.
> > + return -EINVAL; /* reject empty symbol/filter */
>
> Also, before returning an error, use trace_probe_log_err() to
> notice the reason and the place of the error to user.
>
I will log parse failiures with trace_probe_log_err().
> > + }
> > +
> > + rc = register_fprobe(&tf->fp, sym, flt);
> > + kfree(spec);
> > + return rc;
> > + }
> > +
> > + /* Comma list (or single symbol without '!') */
> > + /* First pass: count non-empty tokens */
> > + p = spec;
> > + while (p) {
> > + char *tok = strsep(&p, ",");
> > + if (tok && *strim(tok))
> > + n++;
> > + }
> > +
> > + if (n == 0){
> > + kfree(spec);
> > + return -EINVAL;
> > + }
> > +
> > + /* Allocate array for pointers into spec (callee copies/consumes)
> > */
> > + syms = kcalloc(n, sizeof(*syms), GFP_KERNEL);
> > + if (!syms) {
> > + kfree(spec);
> > + return -ENOMEM;
> > + }
> > +
> > + /* Second pass: fill, skipping empties */
>
> Again, symbol should not have a space.
>
Understood. I will also fix this in v2.
> > + p = spec;
> > + while (p) {
> > + char *tok = strsep(&p, ",");
> > + char *s;
> > +
> > + if (!tok)
> > + break;
> > + s = strim(tok);
> > + if (!*s)
> > + continue;
> > + syms[w++] = s;
> > + }
> > +
> > + /* Dedup in-place */
> > + for (i = 0; i < w; i++){
> > + if (!syms[i])
> > + continue;
> > + for (j = i + 1; j < w; j++) {
> > + if (syms[j] && !strcmp(syms[i], syms[j]))
> > + syms[j] = NULL;
> > + }
>
> I think dedup will be done in ftrace, so we don't need to do this
> costly operation.
>
I see. I will remove the dedup here.
> > + }
> > +
> > + /* Compact */
> > + for (i = 0, j = 0; i < w; i++) {
> > + if (syms[i])
> > + syms[j++] = syms[i];
> > + }
> > + w = j;
> > +
> > + /* After dedup, ensure we still have at least one symbol */
> > + if (w == 0){
> > + kfree(syms);
> > + kfree(spec);
> > + return -EINVAL;
> > + }
> > +
> > + /* Register list or single symbol, using the existing bulk API */
> > + if (w == 1)
> > + rc = register_fprobe(&tf->fp, syms[0], NULL);
>
> Hmm, you might misunderstand this. What you need to do is to classify
> the list of symbols with '!' as nofilter, and others as "filter",
> and pass those as "register_fprobe(&tf->fp, filter, nofilter)".
>
Thank you for the clarification.
I will change as followed:
- tokens prefixed with '!' go to the nofileter list
- all other tokens go to filter list
- pass both to register_fprobe(&tf->fp, filter, nofilter)
> Thank you,
>
> > + else
> > + rc = register_fprobe_syms(&tf->fp, (const char **)syms, w);
> > +
> > + kfree(syms);
> > + kfree(spec);
> > + return rc;
> > + }
> > }
> >
> > /* Internal unregister function - just handle fprobe and flags */
> > --
> > 2.43.0
> >
>
>
> --
> Masami Hiramatsu (Google) <mhira...@kernel.org>
Thank you. Please let me know if you have any questions or concerns.
Best regards,
Ryan Chung
