linux-kernel - Re: [PATCH] perf parse-events: Use strcmp to compare the PMU name

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Message-ID: <20200507164642.GD31109@kernel.org>
Date:   Thu, 7 May 2020 13:46:42 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     "Jin, Yao" <yao.jin@...ux.intel.com>
Cc:     John Garry <john.garry@...wei.com>, Jiri Olsa <jolsa@...hat.com>,
        jolsa@...nel.org, peterz@...radead.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, Linux-kernel@...r.kernel.org,
        ak@...ux.intel.com, kan.liang@...el.com, yao.jin@...el.com,
        "irogers@...gle.com" <irogers@...gle.com>
Subject: Re: [PATCH] perf parse-events: Use strcmp to compare the PMU name

Em Thu, Apr 30, 2020 at 09:38:34PM +0800, Jin, Yao escreveu:
> Hi John, Jiri,
> 
> On 4/30/2020 7:48 PM, John Garry wrote:
> > On 30/04/2020 12:15, Jiri Olsa wrote:
> > 
> > +
> > 
> > > On Thu, Apr 30, 2020 at 09:54:18AM +0100, John Garry wrote:
> > > > On 30/04/2020 09:45, Jiri Olsa wrote:
> > > > > On Thu, Apr 30, 2020 at 08:36:18AM +0800, Jin Yao wrote:
> > > > > > A big uncore event group is split into multiple small groups which
> > > > > > only include the uncore events from the same PMU. This has been
> > > > > > supported in the commit 3cdc5c2cb924a ("perf parse-events: Handle
> > > > > > uncore event aliases in small groups properly").
> > > > > > 
> > > > > > If the event's PMU name starts to repeat, it must be a new event.
> > > > > > That can be used to distinguish the leader from other members.
> > > > > > But now it only compares the pointer of pmu_name
> > > > > > (leader->pmu_name == evsel->pmu_name).
> > > > > > 
> > > > > > If we use "perf stat -M LLC_MISSES.PCIE_WRITE -a" on cascadelakex,
> > > > > > the event list is:
> > > > > > 
> > > > > > evsel->name                    evsel->pmu_name
> > > > > > ---------------------------------------------------------------
> > > > > > unc_iio_data_req_of_cpu.mem_write.part0        uncore_iio_4 (as leader)
> > > > > > unc_iio_data_req_of_cpu.mem_write.part0        uncore_iio_2
> > > > > > unc_iio_data_req_of_cpu.mem_write.part0        uncore_iio_0
> > > > > > unc_iio_data_req_of_cpu.mem_write.part0        uncore_iio_5
> > > > > > unc_iio_data_req_of_cpu.mem_write.part0        uncore_iio_3
> > > > > > unc_iio_data_req_of_cpu.mem_write.part0        uncore_iio_1
> > > > > > unc_iio_data_req_of_cpu.mem_write.part1        uncore_iio_4
> > > > > > ......
> > > > > > 
> > > > > > For the event "unc_iio_data_req_of_cpu.mem_write.part1" with
> > > > > > "uncore_iio_4", it should be the event from PMU "uncore_iio_4".
> > > > > > It's not a new leader for this PMU.
> > > > > > 
> > > > > > But if we use "(leader->pmu_name == evsel->pmu_name)", the check
> > > > > > would be failed and the event is stored to leaders[] as a new
> > > > > > PMU leader.
> > > > > > 
> > > > > > So this patch uses strcmp to compare the PMU name between events.
> > > > > > 
> > > > > > Fixes: 3cdc5c2cb924a ("perf parse-events: Handle uncore
> > > > > > event aliases in small groups properly")
> > > > > > Signed-off-by: Jin Yao <yao.jin@...ux.intel.com>
> > > > > 
> > > > > looks good, any chance we could have automated test
> > > > > for this uncore leader setup logic? like maybe the way
> > > > > John did the pmu-events tests? like test will trigger
> > > > > only when there's the pmu/events in the system
> > > > > 
> > > > > Acked-by: Jiri Olsa <jolsa@...hat.com>
> > > > > 
> > > > > thanks,
> > > > > jirka
> > > > 
> > > > Hi jirka,
> > > > 
> > > > JFYI, this is effectively the same patch as I mentioned to you, which was a
> > > > fix for the same WARN:
> > > > 
> > > > https://lore.kernel.org/linux-arm-kernel/1587120084-18990-2-git-send-email-john.garry@huawei.com/
> > > > 
> > > > 
> > > > but I found that it "fixed" d4953f7ef1a2 ("perf parse-events: Fix 3 use
> > > > after frees found with clang ASANutil/parse-events.c"), based on bisect
> > > > breakage
> > > 
> > > hum right.. sorry I did not recalled that, there's
> > > also the warn removal in here, could you guys also
> > > plz sync on the fixes clauses?
> > 
> > I just thought that it fixes d4953f7ef1a2, as I found that the pointer
> > equality fails from that commit. I assume the parse-events code was
> > sound before then (in that regard). That's all I know :)
> > 
> > Thanks!
> > 
> 
> For 3cdc5c2cb924a, I just think it should use strcmp for pmu_name comparison
> rather than using pointer. But I'm OK to add d4953f7ef1a2 in fixes clauses.
> :)

So, I'm keeping Ian's patch, as I just applied it, and replaced the
fixes clause to:

Fixes: d4953f7ef1a2 ("perf parse-events: Fix 3 use after frees found with clang ASAN")


Would this be ok? Or does John's fix has something else in it (I haven't
checked).

- Arnaldo