From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Riccardo Mancini <rickyman7@gmail.com>
Cc: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
Ian Rogers <irogers@google.com>,
Namhyung Kim <namhyung@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>,
Adrian Hunter <adrian.hunter@intel.com>,
Andi Kleen <ak@linux.intel.com>,
Tommi Rantala <tommi.t.rantala@nokia.com>,
linux-perf-users <linux-perf-users@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] perf ksymbol: fix memory leak: decrease refcount of map and dso
Date: Fri, 4 Jun 2021 15:29:33 -0300 [thread overview]
Message-ID: <YLpxDf6+YOxYI5z3@kernel.org> (raw)
In-Reply-To: <3b8c7c2c5de492c7fbf86df73c43cdb0fbb453df.camel@gmail.com>
Em Fri, Jun 04, 2021 at 05:16:39PM +0200, Riccardo Mancini escreveu:
> Hi,
>
> On Fri, 2021-06-04 at 10:22 -0300, Arnaldo Carvalho de Melo wrote:
> > Em Thu, Jun 03, 2021 at 09:26:40PM -0700, Ian Rogers escreveu:
> > > On Wed, Jun 2, 2021 at 4:15 PM Riccardo Mancini <rickyman7@gmail.com> wrote:
> > > > +++ b/tools/perf/util/machine.c
> > > > @@ -776,6 +776,7 @@ static int machine__process_ksymbol_register(struct
> > > > machine *machine,
> > > > if (dso) {
> > > > dso->kernel = DSO_SPACE__KERNEL;
> > > > map = map__new2(0, dso);
> > > > + dso__put(dso);
> >
> > > Will this cause 2 puts if the map allocation fails? Perhaps this
> > > should be "if (map) dso__put(dso);".
> >
> > I think its just a matter of removing the put in the error path, i.e.
> > the patch becomes what is at the end of this message.
> >
> > I.e. if map__new2() fails, we want to drop the dso reference, and if it
> > works, we already have a reference to it, obtained in map__new2().
>
> Agree.
> I'm sorry for this stupid oversight.
> Should we make it a series including the fix to the issue you pointed out below,
> or should I send you a v2 and fix the other issue in a subsequent patch?
Please send a v2 patch, and then consider starting a new series with the
issues below.
> > But looking at this code now I realize that maps__find() should grab a
> > refcount for the map it returns, because in this
> > machine__process_ksymbol_register() function we use reference that 'map'
> > after the if block, i.e. we use it if it came from maps__find() or if we
> > created it machine__process_ksymbol_register, so there is a possible
> > race where other thread removes it from the list and map__put()s it
> > ending up in map__delete() while we still use it in
> > machine__process_ksymbol_register(), right?
>
> Agree. It should be placed before up_read to avoid races, right?
Yes, we have to grab a refcount while we are sure its not going away,
then return that as the lookup result, whoever receives that refcounted
entry should use it and then drop the refcount.
> Then we would need to see where it's called and add the appropriate map__put.
yes
> In addition, having a look at other possible concurrency issues in map.c:
Its good to have new eyes looking at this, exactly at a time we're
discussing further parallelizing perf :-)
> - maps__for_each_entry should always be called with either read or write lock,
> am I right? It looks like this is not done in certain parts of the code. If such
Right.
> lock is taken, then grabbing the refcount on the looping variable is not needed
> unless we need to return it, right?
Right, returning an entry needs to take a refcount.
> - maps__first and map__next do not grab a refcount and neither a lock. If
> they're used through a lock-protected loop, it's not a problem, but maybe it's
yes
> worth making explicit that they are not to be used directly (through either a
> comment or adding some underscores in their names).
yes, __ in front means, in kernel style, that it does less than the non
__ prefixed, same name, function.
> - maps__empty: should probably take a reader lock.
Indeed.
> - maps__find_symbol: the returned symbol is not protected (the caller does not
> receive a refcount to neither map or dso, so if dso is deleted, his reference to
> the symbol gets invalidated). Depending on how it's being used it might not be a
> problem, but in the general scenario I think it's not thread-safe.
Yes, that function is also problematic.
Thanks for looking into this, please consider sending patches for these
issues,
- Arnaldo
next prev parent reply other threads:[~2021-06-04 18:29 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-02 23:10 [PATCH] perf ksymbol: fix memory leak: decrease refcount of map and dso Riccardo Mancini
2021-06-04 4:26 ` Ian Rogers
2021-06-04 13:22 ` Arnaldo Carvalho de Melo
2021-06-04 15:16 ` Riccardo Mancini
2021-06-04 18:29 ` Arnaldo Carvalho de Melo [this message]
2021-06-12 17:37 ` [PATCH v2] " Riccardo Mancini
2021-06-16 18:12 ` Arnaldo Carvalho de Melo
2021-06-18 10:01 ` [PATCH] " Riccardo Mancini
2021-06-18 13:25 ` Arnaldo Carvalho de Melo
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YLpxDf6+YOxYI5z3@kernel.org \
--to=acme@kernel.org \
--cc=adrian.hunter@intel.com \
--cc=ak@linux.intel.com \
--cc=alexander.shishkin@linux.intel.com \
--cc=arnaldo.melo@gmail.com \
--cc=irogers@google.com \
--cc=jolsa@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-perf-users@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=mingo@redhat.com \
--cc=namhyung@kernel.org \
--cc=peterz@infradead.org \
--cc=rickyman7@gmail.com \
--cc=tommi.t.rantala@nokia.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.