Messages in this thread | | | From | Namhyung Kim <> | Date | Tue, 27 Dec 2022 13:05:54 -0800 | Subject | Re: [PATCH] perf record: Fix coredump with --overwrite and --max-size |
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On Tue, Dec 27, 2022 at 5:10 AM Yang Jihong <yangjihong1@huawei.com> wrote: > > When --overwrite and --max-size options of perf record are used together, > a segmentation fault occurs. The following is an example: > > # perf record -e sched:sched* --overwrite --max-size 1M -a -- sleep 1 > [ perf record: Woken up 1 times to write data ] > perf: Segmentation fault > Obtained 1 stack frames. > [0xc4c67f] > Segmentation fault (core dumped) > > backtrace of the core file is as follows: > > #0 0x0000000000417990 in process_locked_synthesized_event (tool=0x0, event=0x15, sample=0x1de0, machine=0xf8) at builtin-record.c:630 > #1 0x000000000057ee53 in perf_event__synthesize_threads (nr_threads_synthesize=21, mmap_data=<optimized out>, needs_mmap=<optimized out>, machine=0x17ad9b0, process=<optimized out>, tool=0x0) at util/synthetic-events.c:1950 > #2 __machine__synthesize_threads (nr_threads_synthesize=0, data_mmap=<optimized out>, needs_mmap=<optimized out>, process=<optimized out>, threads=0x8, target=0x8, tool=0x0, machine=0x17ad9b0) at util/synthetic-events.c:1936 > #3 machine__synthesize_threads (machine=0x17ad9b0, target=0x8, threads=0x8, needs_mmap=<optimized out>, data_mmap=<optimized out>, nr_threads_synthesize=0) at util/synthetic-events.c:1947 > #4 0x000000000040165d in record__synthesize (tail=<optimized out>, rec=0xbe2520 <record>) at builtin-record.c:2010 > #5 0x0000000000403989 in __cmd_record (argc=<optimized out>, argv=<optimized out>, rec=0xbe2520 <record>) at builtin-record.c:2810 > #6 0x00000000004196ba in record__init_thread_user_masks (rec=0xbe2520 <record>, cpus=0x17a65f0) at builtin-record.c:3837 > #7 record__init_thread_masks (rec=0xbe2520 <record>) at builtin-record.c:3938 > #8 cmd_record (argc=1, argv=0x7ffdd692dc60) at builtin-record.c:4241 > #9 0x00000000004b701d in pager_command_config (var=0x0, value=0x15 <error: Cannot access memory at address 0x15>, data=0x1de0) at perf.c:117 > #10 0x00000000004b732b in get_leaf_frame_caller_aarch64 (sample=0xfffffffb, thread=0x0, usr_idx=<optimized out>) at util/arm64-frame-pointer-unwind-support.c:56 > #11 0x0000000000406331 in execv_dashed_external (argv=0x7ffdd692d9e8) at perf.c:410 > #12 run_argv (argcp=<synthetic pointer>, argv=<synthetic pointer>) at perf.c:431 > #13 main (argc=<optimized out>, argv=0x7ffdd692d9e8) at perf.c:562
I'm not sure this callstack is correct.
> > The reason is that record__bytes_written accesses the freed memory rec->thread_data, > The process is as follows: > __cmd_record > -> record__free_thread_data > -> zfree(&rec->thread_data) // free rec->thread_data > -> record__synthesize > -> perf_event__synthesize_id_index > -> process_synthesized_event > -> record__write > -> record__bytes_written // access rec->thread_data > > In the overwrite scenario, to synthesize non-sample events, > we do not need to check perf size limit.
Hmm.. I think we should prevent this kind of access after record__free_thread_data(). We may set nr_threads to 0 and save the bytes_written for threads separately.
Thanks, Namhyung
> > Fixes: 6d57581659f7 ("perf record: Add support for limit perf output file size") > Signed-off-by: Yang Jihong <yangjihong1@huawei.com> > --- > tools/perf/builtin-record.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c > index 29dcd454b8e2..c5f169150d63 100644 > --- a/tools/perf/builtin-record.c > +++ b/tools/perf/builtin-record.c > @@ -260,7 +260,7 @@ static int record__write(struct record *rec, struct mmap *map __maybe_unused, > else > rec->bytes_written += size; > > - if (record__output_max_size_exceeded(rec) && !done) { > + if (!rec->opts.tail_synthesize && record__output_max_size_exceeded(rec) && !done) { > fprintf(stderr, "[ perf record: perf size limit reached (%" PRIu64 " KB)," > " stopping session ]\n", > record__bytes_written(rec) >> 10); > -- > 2.17.1 >
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