From: Mathieu Poirier <mathieu.poirier@linaro.org>
To: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Suzuki Poulose <suzuki.poulose@arm.com>,
Mike Leach <mike.leach@linaro.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
coresight@lists.linaro.org, Stephen Boyd <swboyd@chromium.org>,
linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCHv2 2/4] coresight: tmc-etf: Fix NULL ptr dereference in tmc_enable_etf_sink_perf()
Date: Wed, 4 Nov 2020 10:03:35 -0700 [thread overview]
Message-ID: <20201104170335.GA2892592@xps15> (raw)
In-Reply-To: <85c285361ce1c71b1a8274493aab9ca7@codeaurora.org>
On Fri, Oct 30, 2020 at 10:56:09PM +0530, Sai Prakash Ranjan wrote:
> Hi Mathieu,
>
> On 2020-10-30 22:18, Mathieu Poirier wrote:
> > On Fri, Oct 30, 2020 at 01:29:56PM +0530, Sai Prakash Ranjan wrote:
> > > Hello guys,
> > >
> > > On 2020-10-24 02:07, Mathieu Poirier wrote:
> > > > On Fri, Oct 23, 2020 at 03:44:16PM +0200, Peter Zijlstra wrote:
> > > > > On Fri, Oct 23, 2020 at 02:29:54PM +0100, Suzuki Poulose wrote:
> > > > > > On 10/23/20 2:16 PM, Peter Zijlstra wrote:
> > > > > > > On Fri, Oct 23, 2020 at 01:56:47PM +0100, Suzuki Poulose wrote:
> > > > >
> > > > > > > > That way another session could use the same sink if it is free. i.e
> > > > > > > >
> > > > > > > > perf record -e cs_etm/@sink0/u --per-thread app1
> > > > > > > >
> > > > > > > > and
> > > > > > > >
> > > > > > > > perf record -e cs_etm/@sink0/u --per-thread app2
> > > > > > > >
> > > > > > > > both can work as long as the sink is not used by the other session.
> > > > > > >
> > > > > > > Like said above, if sink is shared between CPUs, that's going to be a
> > > > > > > trainwreck :/ Why do you want that?
> > > > > >
> > > > > > That ship has sailed. That is how the current generation of systems are,
> > > > > > unfortunately. But as I said, this is changing and there are guidelines
> > > > > > in place to avoid these kind of topologies. With the future
> > > > > > technologies, this will be completely gone.
> > > > >
> > > > > I understand that the hardware is like that, but why do you want to
> > > > > support this insanity in software?
> > > > >
> > > > > If you only allow a single sink user (group) at the same time, your
> > > > > problem goes away. Simply disallow the above scenario, do not allow
> > > > > concurrent sink users if sinks are shared like this.
> > > > >
> > > > > Have the perf-record of app2 above fail because the sink is in-user
> > > > > already.
> > > >
> > > > I agree with you that --per-thread scenarios are easy to deal with, but
> > > > to
> > > > support cpu-wide scenarios events must share a sink (because there is
> > > > one event
> > > > per CPU). CPU-wide support can't be removed because it has been around
> > > > for close to a couple of years and heavily used. I also think using the
> > > > pid of
> > > > the process that created the events, i.e perf, is a good idea. We just
> > > > need to
> > > > agree on how to gain access to it.
> > > >
> > > > In Sai's patch you objected to the following:
> > > >
> > > > > + struct task_struct *task = READ_ONCE(event->owner);
> > > > > +
> > > > > + if (!task || is_kernel_event(event))
> > > >
> > > > Would it be better to use task_nr_pid(current) instead of event->owner?
> > > > The end
> > > > result will be exactly the same. There is also no need to check the
> > > > validity of
> > > > @current since it is a user process.
> > > >
> > >
> > > We have devices deployed where these crashes are seen consistently,
> > > so for some immediate relief, could we atleast get some fix in this
> > > cycle without major design overhaul which would likely take more time.
> > > Perhaps my first patch [1] without any check for owner or
> > > I can post a new version as Suzuki suggested [2] dropping the export
> > > of is_kernel_event(). Then we can always work on top of it based on
> > > the
> > > conclusion of this discussion, we will atleast not have the systems
> > > crash in the meantime, thoughts?
> >
> > For the time being I think [1], exactly the way it is, is a reasonable
> > way
> > forward.
> >
>
> Sure, I just checked now and [1] still applies neatly on top of coresight
> next branch.
>
> [1] https://lore.kernel.org/patchwork/patch/1318098/
I have applied both patches that were part of the set.
>
> Thanks,
> Sai
>
> --
> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
> of Code Aurora Forum, hosted by The Linux Foundation
next prev parent reply other threads:[~2020-11-04 17:03 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-22 10:57 [PATCHv2 0/4] coresight: etf/etb10/etr: Fix NULL pointer dereference crashes Sai Prakash Ranjan
2020-10-22 10:57 ` [PATCHv2 1/4] perf/core: Export is_kernel_event() Sai Prakash Ranjan
2020-10-22 10:57 ` [PATCHv2 2/4] coresight: tmc-etf: Fix NULL ptr dereference in tmc_enable_etf_sink_perf() Sai Prakash Ranjan
2020-10-22 11:32 ` Peter Zijlstra
2020-10-22 12:49 ` Sai Prakash Ranjan
2020-10-22 13:34 ` Peter Zijlstra
2020-10-22 14:23 ` Sai Prakash Ranjan
2020-10-22 13:30 ` Suzuki Poulose
2020-10-22 15:06 ` Peter Zijlstra
2020-10-22 15:32 ` Suzuki Poulose
2020-10-22 21:20 ` Mathieu Poirier
2020-10-23 7:39 ` Peter Zijlstra
2020-10-23 8:49 ` Suzuki Poulose
2020-10-23 9:23 ` Peter Zijlstra
2020-10-23 10:49 ` Suzuki Poulose
2020-10-23 9:41 ` Peter Zijlstra
2020-10-23 10:34 ` Suzuki Poulose
2020-10-23 10:54 ` Peter Zijlstra
2020-10-23 12:56 ` Suzuki Poulose
2020-10-23 13:16 ` Peter Zijlstra
2020-10-23 13:29 ` Suzuki Poulose
2020-10-23 13:44 ` Peter Zijlstra
2020-10-23 20:37 ` Mathieu Poirier
2020-10-30 7:59 ` Sai Prakash Ranjan
2020-10-30 16:48 ` Mathieu Poirier
2020-10-30 17:26 ` Sai Prakash Ranjan
2020-11-04 17:03 ` Mathieu Poirier [this message]
2020-10-22 10:57 ` [PATCHv2 3/4] coresight: etb10: Fix possible NULL ptr dereference in etb_enable_perf() Sai Prakash Ranjan
2020-10-22 10:57 ` [PATCHv2 4/4] coresight: tmc-etr: Fix possible NULL ptr dereference in get_perf_etr_buf_cpu_wide() Sai Prakash Ranjan
2020-10-22 11:10 ` [PATCHv2 0/4] coresight: etf/etb10/etr: Fix NULL pointer dereference crashes Sai Prakash Ranjan
2020-10-22 11:23 ` Sai Prakash Ranjan
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=20201104170335.GA2892592@xps15 \
--to=mathieu.poirier@linaro.org \
--cc=acme@kernel.org \
--cc=alexander.shishkin@linux.intel.com \
--cc=coresight@lists.linaro.org \
--cc=jolsa@redhat.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-arm-msm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=mike.leach@linaro.org \
--cc=mingo@redhat.com \
--cc=namhyung@kernel.org \
--cc=peterz@infradead.org \
--cc=saiprakash.ranjan@codeaurora.org \
--cc=suzuki.poulose@arm.com \
--cc=swboyd@chromium.org \
/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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).