Messages in this thread Patch in this message | | | Date | Thu, 27 Sep 2018 18:02:10 +0200 | From | Jiri Olsa <> | Subject | Re: perf segmentation fault from NULL dereference |
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On Tue, Sep 25, 2018 at 04:53:40PM +0100, John Garry wrote: > Hi, > > I am seeing this perf crash on my arm64-based system: > > root@localhost:~# ./perf_debug_ record -e armv8_pmuv3_0/br_mis_pred/ sleep 1 > perf: Segmentation fault > Obtained 9 stack frames. > ./perf_debug_() [0x4c5ef8] > [0xffff82ba267c] > ./perf_debug_() [0x4bc5a8] > ./perf_debug_() [0x419550] > ./perf_debug_() [0x41a928] > ./perf_debug_() [0x472f58] > ./perf_debug_() [0x473210] > ./perf_debug_() [0x4070f4] > /lib/aarch64-linux-gnu/libc.so.6(__libc_start_main+0xe0) [0xffff8294c8a0] > Segmentation fault (core dumped) > > I find 'cycles' event is fine. > > I bisected the issue to here: > commit bfd8f72c2778f5bd63dc9eb6d23bd7a0d99cff6d (HEAD, refs/bisect/bad) > Author: Andi Kleen <ak@linux.intel.com> > Date: Fri Nov 17 13:42:58 2017 -0800 > > perf record: Synthesize unit/scale/... in event update > > Move the code to synthesize event updates for scale/unit/cpus to a > common utility file, and use it both from stat and record. > > This allows to access scale and other extra qualifiers from perf script. > > Signed-off-by: Andi Kleen <ak@linux.intel.com> > Acked-by: Jiri Olsa <jolsa@kernel.org> > Link: > http://lkml.kernel.org/r/20171117214300.32746-2-andi@firstfloor.org > Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> > > I am suspicious that this is a real issue, as this patch has been in > mainline for some time... > > This simple change fixes the issue me: > diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c > index 91e6d9c..f4fd826 100644 > --- a/tools/perf/util/header.c > +++ b/tools/perf/util/header.c > @@ -3576,7 +3576,7 @@ int perf_event__process_feature(struct perf_tool > *tool, > int max, err; > u16 type; > > - if (!evsel->own_cpus) > + if (!evsel->own_cpus || !(evsel->attr.read_format & PERF_FORMAT_ID)) // > roundabout check for !evsel->id > return 0; > > ev = cpu_map_data__alloc(evsel->own_cpus, &size, &type, &max); > > It turns out that evsel->id is NULL on a call to > perf_event__process_feature(), which upsets this code: > > ev->header.type = PERF_RECORD_EVENT_UPDATE; > ev->header.size = (u16)size; > ev->type = PERF_EVENT_UPDATE__CPUS; > ev->id = evsel->id[0]; > > Please me let me know if a valid issue so we can get a fix in.
yea, I can see how we can get here with event having its own CPUs, and we allocate the id array later at the time we map the event
I wonder instead of skipping on this feature, we should allocate the id array, like below
I did not test that.. need to find the server having event with its own cpus.. also need to make sure evsel->cpus is the way to go in here
thanks, jirka
--- diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c index 1ec1d9bc2d63..fb2a0dab3978 100644 --- a/tools/perf/util/header.c +++ b/tools/perf/util/header.c @@ -29,6 +29,7 @@ #include "symbol.h" #include "debug.h" #include "cpumap.h" +#include "thread_map.h" #include "pmu.h" #include "vdso.h" #include "strbuf.h" @@ -3579,6 +3580,11 @@ perf_event__synthesize_event_update_cpus(struct perf_tool *tool, if (!evsel->own_cpus) return 0; + if (!evsel->id || + perf_evsel__alloc_id(evsel, cpu_map__nr(evsel->cpus), + thread_map__nr(evsel->threads))) + return -ENOMEM; + ev = cpu_map_data__alloc(evsel->own_cpus, &size, &type, &max); if (!ev) return -ENOMEM;
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