Re: [PATCH] perf record: Skip side-band event setup if HAVE_LIBBPF_SUPPORT is not set
From: Jin, Yao
Date: Sun Aug 09 2020 - 20:49:55 EST
Hi Arnaldo,
On 8/7/2020 8:28 PM, Arnaldo Carvalho de Melo wrote:
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@entry=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@xxxxxxxxxx>
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@quaco ~]$ 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@quaco ~]$
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@xxxxxxxxxxxxxxx>
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@entry=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@test:~# ./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@xxxxxxxxxxxxxxx>
Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Jin Yao <yao.jin@xxxxxxxxx>
Cc: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lore.kernel.org/lkml/20200805022937.29184-1-yao.jin@xxxxxxxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
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;
Thanks so much for helping to refine the patch!
Thanks
Jin Yao