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From: Peter Zijlstra <peterz@infradead.org>
To: Suzuki Poulose <suzuki.poulose@arm.com>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>,
	Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>,
	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: Fri, 23 Oct 2020 15:44:16 +0200	[thread overview]
Message-ID: <20201023134416.GA2628@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <728fd89c-78f2-0c5c-0443-c91c62b02f0e@arm.com>

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.

Only if the hardware has per-CPU sinks can you allow this.

WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Suzuki Poulose <suzuki.poulose@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>,
	Mathieu Poirier <mathieu.poirier@linaro.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	linux-arm-msm@vger.kernel.org, coresight@lists.linaro.org,
	linux-kernel@vger.kernel.org,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Stephen Boyd <swboyd@chromium.org>,
	Ingo Molnar <mingo@redhat.com>,
	Namhyung Kim <namhyung@kernel.org>, Jiri Olsa <jolsa@redhat.com>,
	linux-arm-kernel@lists.infradead.org,
	Mike Leach <mike.leach@linaro.org>
Subject: Re: [PATCHv2 2/4] coresight: tmc-etf: Fix NULL ptr dereference in tmc_enable_etf_sink_perf()
Date: Fri, 23 Oct 2020 15:44:16 +0200	[thread overview]
Message-ID: <20201023134416.GA2628@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <728fd89c-78f2-0c5c-0443-c91c62b02f0e@arm.com>

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.

Only if the hardware has per-CPU sinks can you allow this.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2020-10-23 13:44 UTC|newest]

Thread overview: 63+ 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 ` 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   ` Sai Prakash Ranjan
2020-10-31  7:35   ` kernel test robot
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 10:57   ` Sai Prakash Ranjan
2020-10-22 11:32   ` Peter Zijlstra
2020-10-22 11:32     ` Peter Zijlstra
2020-10-22 12:49     ` Sai Prakash Ranjan
2020-10-22 12:49       ` Sai Prakash Ranjan
2020-10-22 13:34       ` Peter Zijlstra
2020-10-22 13:34         ` Peter Zijlstra
2020-10-22 14:23         ` Sai Prakash Ranjan
2020-10-22 14:23           ` Sai Prakash Ranjan
2020-10-22 13:30     ` Suzuki Poulose
2020-10-22 13:30       ` Suzuki Poulose
2020-10-22 15:06       ` Peter Zijlstra
2020-10-22 15:06         ` Peter Zijlstra
2020-10-22 15:32         ` Suzuki Poulose
2020-10-22 15:32           ` Suzuki Poulose
2020-10-22 21:20           ` Mathieu Poirier
2020-10-22 21:20             ` Mathieu Poirier
2020-10-23  7:39             ` Peter Zijlstra
2020-10-23  7:39               ` Peter Zijlstra
2020-10-23  8:49               ` Suzuki Poulose
2020-10-23  8:49                 ` Suzuki Poulose
2020-10-23  9:23                 ` Peter Zijlstra
2020-10-23  9:23                   ` Peter Zijlstra
2020-10-23 10:49                   ` Suzuki Poulose
2020-10-23 10:49                     ` Suzuki Poulose
2020-10-23  9:41                 ` Peter Zijlstra
2020-10-23  9:41                   ` Peter Zijlstra
2020-10-23 10:34                   ` Suzuki Poulose
2020-10-23 10:34                     ` Suzuki Poulose
2020-10-23 10:54                     ` Peter Zijlstra
2020-10-23 10:54                       ` Peter Zijlstra
2020-10-23 12:56                       ` Suzuki Poulose
2020-10-23 12:56                         ` Suzuki Poulose
2020-10-23 13:16                         ` Peter Zijlstra
2020-10-23 13:16                           ` Peter Zijlstra
2020-10-23 13:29                           ` Suzuki Poulose
2020-10-23 13:29                             ` Suzuki Poulose
2020-10-23 13:44                             ` Peter Zijlstra [this message]
2020-10-23 13:44                               ` Peter Zijlstra
2020-10-23 20:37                               ` Mathieu Poirier
2020-10-23 20:37                                 ` Mathieu Poirier
2020-10-30  7:59                                 ` Sai Prakash Ranjan
2020-10-30  7:59                                   ` Sai Prakash Ranjan
2020-10-30 16:48                                   ` Mathieu Poirier
2020-10-30 16:48                                     ` Mathieu Poirier
2020-10-30 17:26                                     ` Sai Prakash Ranjan
2020-10-30 17:26                                       ` Sai Prakash Ranjan
2020-11-04 17:03                                       ` Mathieu Poirier
2020-11-04 17:03                                         ` Mathieu Poirier
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   ` 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 10:57   ` 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 11:10   ` Sai Prakash Ranjan
2020-10-22 11:23   ` Sai Prakash Ranjan
2020-10-22 11:23     ` Sai Prakash Ranjan

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