Messages in this thread | | | Subject | Re: [PATCH v2] perf record: Fix coredump with --overwrite and --max-size | From | Yang Jihong <> | Date | Fri, 13 Jan 2023 14:53:04 +0800 |
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Hello,
On 2023/1/11 3:21, Namhyung Kim wrote: > On Sun, Jan 8, 2023 at 6:47 PM Yang Jihong <yangjihong1@huawei.com> wrote: >> >> Hello, >> >> On 2023/1/7 5:12, Namhyung Kim wrote: >>> Hello, >>> >>> On Wed, Jan 4, 2023 at 8:09 PM Yang Jihong <yangjihong1@huawei.com> wrote: >>>> >>>> Hello, >>>> >>>> On 2023/1/4 0:50, Namhyung Kim wrote: >>>>> On Mon, Jan 2, 2023 at 8:20 AM Arnaldo Carvalho de Melo <acme@kernel.org> wrote: >>>>>> >>>>>> Em Thu, Dec 29, 2022 at 12:47:28PM +0000, Yang Jihong escreveu: >>>>>>> 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 >>>>>>> >>>>>>> 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 >>>>>>> >>>>>>> we only need to check the value of done first. >>>>>>> Also add variable check in record__bytes_written for code hardening, >>>>>>> and save bytes_written separately to reduce one calculation. >>>>>>> >>>>>>> Fixes: 6d57581659f7 ("perf record: Add support for limit perf output file size") >>>>>>> Signed-off-by: Yang Jihong <yangjihong1@huawei.com> >>>>>>> --- >>>>>>> >>>>>>> Changes since v1: >>>>>>> - Add variable check in record__bytes_written for code hardening. >>>>>>> - Save bytes_written separately to reduce one calculation. >>>>>>> - Remove rec->opts.tail_synthesize check. >>>>>> >>>>>> Namhyung, are you ok with this now? >>>>>> >>>>>> - Arnaldo >>>>>> >>>>>>> tools/perf/builtin-record.c | 26 +++++++++++++++++--------- >>>>>>> 1 file changed, 17 insertions(+), 9 deletions(-) >>>>>>> >>>>>>> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c >>>>>>> index 29dcd454b8e2..acba9e43e519 100644 >>>>>>> --- a/tools/perf/builtin-record.c >>>>>>> +++ b/tools/perf/builtin-record.c >>>>>>> @@ -230,16 +230,29 @@ static u64 record__bytes_written(struct record *rec) >>>>>>> u64 bytes_written = rec->bytes_written; >>>>>>> struct record_thread *thread_data = rec->thread_data; >>>>>>> >>>>>>> + if (thread_data == NULL) >>>>>>> + return bytes_written; >>>>>>> + >>>>> >>>>> Then it won't count bytes written by threads, right? >>>>> I think it needs to be saved somewhere. >>>>> >>>> I'm not sure here. Can you explain it more clearly, thanks :) >>>> I can modify it accordingly. >>>> >>>> I think if thread_data == NULL, it is not thread data. >>>> In this case, we just return rec->bytes_written. >>> >>> It can be thread data but freed before tail synthesis, right? >>> In that case, I think it needs to add bytes_written by threads >>> to calculate the correct data size. >> Em... In the __cmd_record function, record__stop_threads is called >> before record__free_thread_data, so if the thread has been freed, there >> will be no thread data. >> I think it's okay to ignore the situation you mentioned above. > > Right, the thread data is already freed, but we need the size. > > I think it didn't (and won't) update to rec->bytes_written for the data > written by the threads (data.X file) because it's only for the main > 'data' file. So record__bytes_written() will return a smaller number > after the threads are gone. But I think it should return the total > data size. > Yes, the total data size including data.X file should be returned here to fit the semantics, so there's a problem here, too. will fix in next version.
Thanks, Yang
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