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Date: Fri, 7 Aug 2020 09:28:40 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Jin Yao <yao.jin@...ux.intel.com>
Cc: 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
Subject: Re: [PATCH] perf record: Skip side-band event setup if
HAVE_LIBBPF_SUPPORT is not set
Em Fri, Aug 07, 2020 at 09:16:29AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Fri, Aug 07, 2020 at 09:09:56AM -0300, Arnaldo Carvalho de Melo escreveu:
> > Em Fri, Aug 07, 2020 at 09:08:24AM -0300, Arnaldo Carvalho de Melo escreveu:
> > > Em Thu, Aug 06, 2020 at 09:43:57PM +0200, Jiri Olsa escreveu:
> > > > On Wed, Aug 05, 2020 at 10:29:37AM +0800, Jin Yao wrote:
> > > > > We received an error report that perf-record caused 'Segmentation fault'
> > > > > on a newly system (e.g. on the new installed ubuntu).
> > > > >
> > > > > (gdb) backtrace
> > > > > #0 __read_once_size (size=4, res=<synthetic pointer>, p=0x14) at /root/0-jinyao/acme/tools/include/linux/compiler.h:139
> > > > > #1 atomic_read (v=0x14) at /root/0-jinyao/acme/tools/include/asm/../../arch/x86/include/asm/atomic.h:28
> > > > > #2 refcount_read (r=0x14) at /root/0-jinyao/acme/tools/include/linux/refcount.h:65
> > > > > #3 perf_mmap__read_init (map=map@...ry=0x0) at mmap.c:177
> > > > > #4 0x0000561ce5c0de39 in perf_evlist__poll_thread (arg=0x561ce68584d0) at util/sideband_evlist.c:62
> > > > > #5 0x00007fad78491609 in start_thread (arg=<optimized out>) at pthread_create.c:477
> > > > > #6 0x00007fad7823c103 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95
> > > >
> > > > hum, I recall discussing the same issue,
> > > > I thought it was already fixed :-\ in any case:
> > > >
> > > > Acked-by: Jiri Olsa <jolsa@...hat.com>
> > >
> > > I added this:
> > >
> > > Fixes: 23cbb41c939a ("perf record: Move side band evlist setup to separate routine")
> > >
> > > To help this fixe go back to a few stable kernels. Technically the
> > > problem was introduced much earlier, when the side band thread was
> > > added, but then this would require more cherry-picking of patches and
> > > since we have a workaround, i.e. build with libbpf, I think this is
> > > enough.
> >
> > I backtrack on that, as the sideband event is not just for BPF... The
> > switch-output-event code uses it as well, so it can't be dependent on
> > LIBBPF being built...
> >
> > I'll see what I can do
>
> So this is the change I made, the side band thread is may have been
> already created by
>
> [acme@...co ~]$ perf record -h switch-output-event
>
> Usage: perf record [<options>] [<command>]
> or: perf record [<options>] -- <command> [<options>]
>
> --switch-output-event <switch output event>
> switch output event selector. use 'perf list' to list available events
>
> [acme@...co ~]$
>
> I'm doing some extra checking now on your report, and the patch below
> has skews because it clashed with the clockid patches by Jiri so I had
> to resolve its merge.
Sorry, I resent your patch, doh, here is the end result, with my change,
its ok to call perf_evlist__start_sb_thread() with a NULL evlist, it'll
just return 0.
- Arnald
commit b13536a7e93680625094beb18cdce4ae47a3dbfb
Author: Jin Yao <yao.jin@...ux.intel.com>
Date: Wed Aug 5 10:29:37 2020 +0800
perf record: Skip side-band event setup if HAVE_LIBBPF_SUPPORT is not set
We received an error report that perf-record caused 'Segmentation fault'
on a newly system (e.g. on the new installed ubuntu).
(gdb) backtrace
#0 __read_once_size (size=4, res=<synthetic pointer>, p=0x14) at /root/0-jinyao/acme/tools/include/linux/compiler.h:139
#1 atomic_read (v=0x14) at /root/0-jinyao/acme/tools/include/asm/../../arch/x86/include/asm/atomic.h:28
#2 refcount_read (r=0x14) at /root/0-jinyao/acme/tools/include/linux/refcount.h:65
#3 perf_mmap__read_init (map=map@...ry=0x0) at mmap.c:177
#4 0x0000561ce5c0de39 in perf_evlist__poll_thread (arg=0x561ce68584d0) at util/sideband_evlist.c:62
#5 0x00007fad78491609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#6 0x00007fad7823c103 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95
The root cause is, evlist__add_bpf_sb_event() just returns 0 if
HAVE_LIBBPF_SUPPORT is not defined (inline function path). So it will
not create a valid evsel for side-band event.
But perf-record still creates BPF side band thread to process the
side-band event, then the error happpens.
We can reproduce this issue by removing the libelf-dev. e.g.
1. apt-get remove libelf-dev
2. perf record -a -- sleep 1
root@...t:~# ./perf record -a -- sleep 1
perf: Segmentation fault
Obtained 6 stack frames.
./perf(+0x28eee8) [0x5562d6ef6ee8]
/lib/x86_64-linux-gnu/libc.so.6(+0x46210) [0x7fbfdc65f210]
./perf(+0x342e74) [0x5562d6faae74]
./perf(+0x257e39) [0x5562d6ebfe39]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x9609) [0x7fbfdc990609]
/lib/x86_64-linux-gnu/libc.so.6(clone+0x43) [0x7fbfdc73b103]
Segmentation fault (core dumped)
To fix this issue,
1. We either install the missing libraries to let HAVE_LIBBPF_SUPPORT
be defined.
e.g. apt-get install libelf-dev and install other related libraries.
2. Use this patch to skip the side-band event setup if HAVE_LIBBPF_SUPPORT
is not set.
Committer notes:
The side band thread is not used just with BPF, it is also used with
--switch-output-event, so narrow the ifdef to the BPF specific part.
Fixes: 23cbb41c939a ("perf record: Move side band evlist setup to separate routine")
Signed-off-by: Jin Yao <yao.jin@...ux.intel.com>
Acked-by: Jiri Olsa <jolsa@...nel.org>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Andi Kleen <ak@...ux.intel.com>
Cc: Jin Yao <yao.jin@...el.com>
Cc: Kan Liang <kan.liang@...ux.intel.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Link: http://lore.kernel.org/lkml/20200805022937.29184-1-yao.jin@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 7d97c8e9f7f9..f91352f847c0 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -1531,7 +1531,7 @@ static int record__setup_sb_evlist(struct record *rec)
evlist__set_cb(rec->sb_evlist, record__process_signal_event, rec);
rec->thread_id = pthread_self();
}
-
+#ifdef HAVE_LIBBPF_SUPPORT
if (!opts->no_bpf_event) {
if (rec->sb_evlist == NULL) {
rec->sb_evlist = evlist__new();
@@ -1547,7 +1547,7 @@ static int record__setup_sb_evlist(struct record *rec)
return -1;
}
}
-
+#endif
if (perf_evlist__start_sb_thread(rec->sb_evlist, &rec->opts.target)) {
pr_debug("Couldn't start the BPF side band thread:\nBPF programs starting from now on won't be annotatable\n");
opts->no_bpf_event = true;
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