linux-kernel - Re: [PATCH V2 linux-next] perf test: Subtest Exclude disjoint subcmd names fails

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Message-ID: <38a7bed7-1272-40a5-8612-6be20d9493ef@linux.ibm.com>
Date: Thu, 22 Jan 2026 11:48:31 +0100
From: Thomas Richter <tmricht@...ux.ibm.com>
To: Ian Rogers <irogers@...gle.com>,
        "Jayaramappa, Srilakshmi" <sjayaram@...mai.com>
Cc: linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-perf-users@...r.kernel.org, acme@...nel.org, namhyung@...nel.org,
        agordeev@...ux.ibm.com, gor@...ux.ibm.com, sumanthk@...ux.ibm.com,
        hca@...ux.ibm.com, japo@...ux.ibm.com
Subject: Re: [PATCH V2 linux-next] perf test: Subtest Exclude disjoint subcmd
 names fails

On 1/21/26 17:14, Ian Rogers wrote:
> On Wed, Jan 21, 2026 at 8:12 AM Ian Rogers <irogers@...gle.com> wrote:
>>
>> On Wed, Jan 21, 2026 at 12:24 AM Thomas Richter <tmricht@...ux.ibm.com> wrote:
>>>
>>> V1 --> V2: Add linux next repository
>>>            s/needed/unneeded/ in commit message
>>>
>>> The perf test case 'libsubcmd help tests', subtest
>>> 'Exclude disjoint subcmd names' fails all the time.
>>>
>>> Root case is a special case of sorted input which the exclude_cmds()
>>> in libsubcmd can not handle. Assume the following inputs:
>>> cmds = { X, Y, Z } and excludes = { A, B }.
>>>
>>> This leads to
>>>  ci  cj  ei   cmds-name  excludes
>>>  ----------|--------------------
>>>  0   0   0 |     X         A       :    cmp > 0, ei++
>>>  0   0   1 |     X         B       :    cmp > 0, ei++
>>>
>>> At this point, the loop is terminated due to ei == excludes->cnt.
>>> The for-loop now checks for trailing names which had to be deleted.
>>> But the first entry points to a name: cmds->names[0].name == "X"
>>> and this is a valid entry.
>>>
>>> This is the case when all commands listed in excludes are less than
>>> all commands listed in cmds.
>>> Only check for existing names when cmds list was changed, that is ci != cj.
>>>
>>> Also remove an unneeded if (cmp > 0).
>>>
>>> -
>>> Output before:
>>>  # ./perf test -F 68
>>>  68.1: Load subcmd names                           : Ok
>>>  68.2: Uniquify subcmd names                       : Ok
>>>  68.3: Exclude duplicate subcmd names              : Ok
>>>  perf: help.c:112: exclude_cmds: Assertion `cmds->names[ci] == NULL' \
>>>         failed.
>>>  Aborted                    ./perf test -F 68
>>>
>>> Output after:
>>>  # ./perf test -F 68
>>>  68.1: Load subcmd names                           : Ok
>>>  68.2: Uniquify subcmd names                       : Ok
>>>  68.3: Exclude duplicate subcmd names              : Ok
>>>  68.4: Exclude disjoint subcmd names               : Ok
>>>
>>> Fixes: 1fdf938168c4 ("perf tools: Fix use-after-free in help_unknown_cmd()")
>>> Cc: Namhyung Kim <namhyung@...nel.org>
>>> Cc: Ian Rogers <irogers@...gle.com>
>>> Signed-off-by: Thomas Richter <tmricht@...ux.ibm.com>
>>
>> Thanks Thomas!
>>
>> I tried to apply this on a perf-tools-next tree but it fails. Looking
>> into the git logs I see on linux-next:
>> https://web.git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/log/tools/lib/subcmd/help.c
>> the last patch is:
>> 2025-09-12 perf subcmd: avoid crash in exclude_cmds when excludes is empty
>> In perf-tools-next:
>> https://web.git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/log/tools/lib/subcmd/help.c?h=tmp.perf-tools-next
>> I see:
>> 8 days libsubcmd: Fix null intersection case in exclude_cmds()
>> 2025-09-12 perf subcmd: avoid crash in exclude_cmds when excludes is empty
>>
>> The test I wrote was to give coverage for  Sri Jayaramappa's fix:
>> https://lore.kernel.org/r/20251202213632.2873731-1-sjayaram@akamai.com
>>
>> I wonder if we've put the test into linux-next but not Sri's fix, well
>> that's what it looks like to me.
>>
>> Now that we have both your fix and Sri's fix, and they differ :-) I'm
>> wondering how to resolve the differences.
> 
> Sorry, resending as I got Sri's email address wrong.
> Ian
> 
Hi Ian, Jayaramappa,

I have looked at both patches and Jayaramappa's patch is already
in perf-tool-next and solves the issue too. I am fine with this one.
So lets simply drop mine.

Thanks Thomas
-- 
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
IBM Deutschland Research & Development GmbH

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