Messages in this thread Patch in this message |  | | From | John Garry <> | Subject | perf segmentation fault from NULL dereference | Date | Tue, 25 Sep 2018 16:53:40 +0100 |
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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.
Apologies for crying wolf if I'm off the mark.
Cheers, John
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