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Subject: Re: [PATCH v2] perf record: Fix coredump with --overwrite and
 --max-size
To:     Namhyung Kim <namhyung@kernel.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>
CC:     <peterz@infradead.org>, <mingo@redhat.com>, <mark.rutland@arm.com>,
        <alexander.shishkin@linux.intel.com>, <jolsa@kernel.org>,
        <jiwei.sun@windriver.com>, <linux-perf-users@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
References: <20221229124728.66515-1-yangjihong1@huawei.com>
 <Y7MEWK/z19QCaNoi@kernel.org>
 <CAM9d7cjcWKBephb5p9ZPU2+wDAz04DYQJoKczORioD=es10hPw@mail.gmail.com>
From:   Yang Jihong <yangjihong1@huawei.com>
Message-ID: <c65f89ef-173c-b828-f3b2-266387903149@huawei.com>
Date:   Thu, 5 Jan 2023 12:09:17 +0800
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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.

Thanks,
Yang