linux-kernel - Re: [PATCH] selftests/ftrace: Fix event filter target

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Date: Tue, 26 Mar 2024 13:24:47 -0600
From: Shuah Khan <skhan@...uxfoundation.org>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
 Mark Rutland <mark.rutland@....com>, Shuah Khan <shuah@...nel.org>
Cc: linux-kernel@...r.kernel.org, aishwarya.tcv@....com,
 linux-kselftest@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 mathieu.desnoyers@...icios.com, rostedt@...dmis.org,
 Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH] selftests/ftrace: Fix event filter target_func selection

On 3/20/24 18:09, Masami Hiramatsu (Google) wrote:
> On Wed, 20 Mar 2024 14:18:44 +0000
> Mark Rutland <mark.rutland@....com> wrote:
> 
>> The event filter function test has been failing in our internal test
>> farm:
>>
>> | # not ok 33 event filter function - test event filtering on functions
>>
>> Running the test in verbose mode indicates that this is because the test
>> erroneously determines that kmem_cache_free() is the most common caller
>> of kmem_cache_free():
>>
>>    # # + cut -d: -f3 trace
>>    # # + sed s/call_site=([^+]*)+0x.*/1/
>>    # # + sort
>>    # # + uniq -c
>>    # # + sort
>>    # # + tail -n 1
>>    # # + sed s/^[ 0-9]*//
>>    # # + target_func=kmem_cache_free
>>
>> .. and as kmem_cache_free() doesn't call itself, setting this as the
>> filter function for kmem_cache_free() results in no hits, and
>> consequently the test fails:
>>
>>    # # + grep kmem_cache_free trace
>>    # # + grep kmem_cache_free
>>    # # + wc -l
>>    # # + hitcnt=0
>>    # # + grep kmem_cache_free trace
>>    # # + grep -v kmem_cache_free
>>    # # + wc -l
>>    # # + misscnt=0
>>    # # + [ 0 -eq 0 ]
>>    # # + exit_fail
>>
>> This seems to be because the system in question has tasks with ':' in
>> their name (which a number of kernel worker threads have). These show up
>> in the trace, e.g.
>>
>>    test:.sh-1299    [004] .....  2886.040608: kmem_cache_free: call_site=putname+0xa4/0xc8 ptr=000000000f4d22f4 name=names_cache
>>
>> .. and so when we try to extact the call_site with:
>>
>>    cut -d: -f3 trace | sed 's/call_site=\([^+]*\)+0x.*/\1/'
>>
>> .. the 'cut' command will extrace the column containing
>> 'kmem_cache_free' rather than the column containing 'call_site=...', and
>> the 'sed' command will leave this unchanged. Consequently, the test will
>> decide to use 'kmem_cache_free' as the filter function, resulting in the
>> failure seen above.
>>
>> Fix this by matching the 'call_site=<func>' part specifically to extract
>> the function name.
>>
> 
> Looks good to me.
> 
> Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> 
> I think this should be a fix because test task name can have ':'.
> 
> Fixes: eb50d0f250e9 ("selftests/ftrace: Choose target function for filter test from samples")
> Cc: stable@...r.kernel.org
> 
> Shuah, can you pick this as a fix?
> 

Applied to linux-ksleftest fixes for next rc

thanks,
-- Shuah