Re: [PATCH] selftests/ftrace: Fix event filter target_func selection

[Shuah Khan]

On 3/20/24 18:09, Masami Hiramatsu (Google) wrote:
> On Wed, 20 Mar 2024 14:18:44 +0000
> Mark Rutland <mark.rutland@xxxxxxx> 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@xxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxx
>
> Shuah, can you pick this as a fix?

Applied to linux-ksleftest fixes for next rc

thanks,
-- Shuah