linux-kernel - Re: [PATCH v2 03/14] perf report: create real callchain entries for inlined frames

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Message-ID: <CAM9d7ch7Lc7yfMRTrHKZnBop05cYNDA_kb+Hx6bznC-t6EOAUA@mail.gmail.com>
Date:   Fri, 8 Sep 2017 00:16:34 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Milian Wolff <milian.wolff@...b.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jin Yao <yao.jin@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <Linux-kernel@...r.kernel.org>,
        linux-perf-users <linux-perf-users@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        David Ahern <dsahern@...il.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>, kernel-team@....com
Subject: Re: [PATCH v2 03/14] perf report: create real callchain entries for
 inlined frames

On Fri, Sep 8, 2017 at 12:05 AM, Milian Wolff <milian.wolff@...b.com> wrote:
> On Thursday, September 7, 2017 4:58:53 PM CEST Namhyung Kim wrote:
>> Hi Milian,
>
> Hey Namhyung!
>
>> > > > > @@ -511,10 +563,63 @@ void inline_node__delete(struct inline_node
>> > > > > *node)
>> > > > >
>> > > > >       list_for_each_entry_safe(ilist, tmp, &node->val, list) {
>> > > > >
>> > > > >               list_del_init(&ilist->list);
>> > > > >
>> > > > > -             zfree(&ilist->filename);
>> > > > > -             zfree(&ilist->funcname);
>> > > > > +             zfree(&ilist->srcline);
>> > > > > +             // only the inlined symbols are owned by the list
>> > > > > +             if (ilist->symbol && ilist->symbol->inlined)
>> > > > > +                     symbol__delete(ilist->symbol);
>> > > >
>> > > > Existing symbols are released at this moment.
>> > >
>> > > Thanks for the review, I'll try to look into these issues once I have
>> > > more
>> > > time again.
>> >
>> > OK, so I just dug into this part of the patch again. I don't think it's
>> > actually a problem after all:
>> >
>> > When an inline node reuses the real symbol, that symbol won't have its
>> > `inlined` member set to true. Thus these symbols will never get deleted by
>> > inline_node__delete.
>>
>> But ilist->symbol is a dangling pointer so accessing ->inlined would
>> be a problem, no?
>
> Sorry, but I can't follow. Why would it be a dangling pointer? Note, again,
> that I've tested this with both valgrind and ASAN and neither reports any
> issues about this code.

IIUC, ilist->symbol can point an existing symbol.  And all existing
symbols are freed before calling inline_node__delete().  I don't know
why valgrind or asan didn't catch anything.. maybe I'm missing
something.

-- 
Thanks,
Namhyung