Subject: Re: [PATCH v3] perf record: Fix segfault with --overwrite and
 --max-size
To:     Namhyung Kim <namhyung@kernel.org>
CC:     <acme@kernel.org>, <linux-perf-users@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <peterz@infradead.org>,
        <mingo@redhat.com>, <mark.rutland@arm.com>,
        <alexander.shishkin@linux.intel.com>, <jolsa@kernel.org>,
        <jiwei.sun@windriver.com>
References: <20230113073803.102950-1-yangjihong1@huawei.com>
 <29a8e0bc-e90b-b371-962b-58a4b8c87f20@huawei.com>
 <ee213278-7e76-586b-0564-843dc7a3c84f@huawei.com>
 <CAM9d7cj1v09Q0_AF2Oaa4+UU_YWB8OaaoeOZ-igoMTTFg4VZGg@mail.gmail.com>
From:   Yang Jihong <yangjihong1@huawei.com>
Message-ID: <0c93a024-b60c-8ea6-37a3-a55e951dbd12@huawei.com>
Date:   Mon, 6 Feb 2023 11:40:32 +0800
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Hello,

On 2023/2/6 10:44, Namhyung Kim wrote:
> Hello,
> 
> On Sun, Feb 5, 2023 at 5:29 PM Yang Jihong <yangjihong1@huawei.com> wrote:
>>
>> Hello,
>>
>> Ping again, please take time to review, thanks.
> 
> Sorry for the late reply.  Now it looks good to me.
Thanks for the review.

Thanks,
Yang.
> 
>>
>>
>> Thanks,
>> Yang
>>
>>
>> On 2023/1/28 9:27, Yang Jihong wrote:
>>> Hello,
>>>
>>> The data written by the thread (data.X file) has been saved as
>>> recommended in v2 patch. Please check whether it is feasible. Thank you.
>>>
>>> Thanks,
>>> Yang
>>>
>>> On 2023/1/13 15:38, Yang Jihong 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 1K -a -- sleep 1
>>>>     [ perf record: Woken up 1 times to write data ]
>>>>     perf: Segmentation fault
>>>>     Obtained 12 stack frames.
>>>>     ./perf/perf(+0x197673) [0x55f99710b673]
>>>>     /lib/x86_64-linux-gnu/libc.so.6(+0x3ef0f) [0x7fa45f3cff0f]
>>>>     ./perf/perf(+0x8eb40) [0x55f997002b40]
>>>>     ./perf/perf(+0x1f6882) [0x55f99716a882]
>>>>     ./perf/perf(+0x794c2) [0x55f996fed4c2]
>>>>     ./perf/perf(+0x7b7c7) [0x55f996fef7c7]
>>>>     ./perf/perf(+0x9074b) [0x55f99700474b]
>>>>     ./perf/perf(+0x12e23c) [0x55f9970a223c]
>>>>     ./perf/perf(+0x12e54a) [0x55f9970a254a]
>>>>     ./perf/perf(+0x7db60) [0x55f996ff1b60]
>>>>     /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe6)
>>>> [0x7fa45f3b2c86]
>>>>     ./perf/perf(+0x7dfe9) [0x55f996ff1fe9]
>>>>     Segmentation fault (core dumped)
>>>>
>>>> backtrace of the core file is as follows:
>>>>
>>>>     (gdb) bt
>>>>     #0  record__bytes_written (rec=0x55f99755a200 <record>) at
>>>> builtin-record.c:234
>>>>     #1  record__output_max_size_exceeded (rec=0x55f99755a200 <record>)
>>>> at builtin-record.c:242
>>>>     #2  record__write (map=0x0, size=12816, bf=0x55f9978da2e0,
>>>> rec=0x55f99755a200 <record>) at builtin-record.c:263
>>>>     #3  process_synthesized_event (tool=tool@entry=0x55f99755a200
>>>> <record>, event=event@entry=0x55f9978da2e0, sample=sample@entry=0x0,
>>>> machine=machine@entry=0x55f997893658) at builtin-record.c:618
>>>>     #4  0x000055f99716a883 in __perf_event__synthesize_id_index
>>>> (tool=tool@entry=0x55f99755a200 <record>,
>>>> process=process@entry=0x55f997002aa0 <process_synthesized_event>,
>>>> evlist=0x55f9978928b0, machine=machine@entry=0x55f997893658,
>>>>         from=from@entry=0) at util/synthetic-events.c:1895
>>>>     #5  0x000055f99716a91f in perf_event__synthesize_id_index
>>>> (tool=tool@entry=0x55f99755a200 <record>,
>>>> process=process@entry=0x55f997002aa0 <process_synthesized_event>,
>>>> evlist=<optimized out>, machine=machine@entry=0x55f997893658)
>>>>         at util/synthetic-events.c:1905
>>>>     #6  0x000055f996fed4c3 in record__synthesize (tail=tail@entry=true,
>>>> rec=0x55f99755a200 <record>) at builtin-record.c:1997
>>>>     #7  0x000055f996fef7c8 in __cmd_record (argc=argc@entry=2,
>>>> argv=argv@entry=0x7ffc67551260, rec=0x55f99755a200 <record>) at
>>>> builtin-record.c:2802
>>>>     #8  0x000055f99700474c in cmd_record (argc=<optimized out>,
>>>> argv=0x7ffc67551260) at builtin-record.c:4258
>>>>     #9  0x000055f9970a223d in run_builtin (p=0x55f997564d88
>>>> <commands+264>, argc=10, argv=0x7ffc67551260) at perf.c:330
>>>>     #10 0x000055f9970a254b in handle_internal_command (argc=10,
>>>> argv=0x7ffc67551260) at perf.c:384
>>>>     #11 0x000055f996ff1b61 in run_argv (argcp=<synthetic pointer>,
>>>> argv=<synthetic pointer>) at perf.c:428
>>>>     #12 main (argc=<optimized out>, argv=0x7ffc67551260) 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 add a member variable "thread_bytes_written" in the struct "record"
>>>> to save the data size written by the threads.
>>>>
>>>> Fixes: 6d57581659f7 ("perf record: Add support for limit perf output
>>>> file size")
>>>> Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
> 
> Acked-by: Namhyung Kim <namhyung@kernel.org>
> 
> Thanks,
> Namhyung
> 
> 
>>>> ---
>>>>
>>>> Changes since v2:
>>>>    - Save data size written by threads to calculate the correct total
>>>> data size.
>>>>    - Update commit message.
>>>>
>>>> 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.
>>>>
>>>>    tools/perf/builtin-record.c | 16 ++++++----------
>>>>    1 file changed, 6 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
>>>> index 29dcd454b8e2..8374117e66f6 100644
>>>> --- a/tools/perf/builtin-record.c
>>>> +++ b/tools/perf/builtin-record.c
>>>> @@ -154,6 +154,7 @@ struct record {
>>>>        struct perf_tool    tool;
>>>>        struct record_opts    opts;
>>>>        u64            bytes_written;
>>>> +    u64            thread_bytes_written;
>>>>        struct perf_data    data;
>>>>        struct auxtrace_record    *itr;
>>>>        struct evlist    *evlist;
>>>> @@ -226,14 +227,7 @@ static bool switch_output_time(struct record *rec)
>>>>    static u64 record__bytes_written(struct record *rec)
>>>>    {
>>>> -    int t;
>>>> -    u64 bytes_written = rec->bytes_written;
>>>> -    struct record_thread *thread_data = rec->thread_data;
>>>> -
>>>> -    for (t = 0; t < rec->nr_threads; t++)
>>>> -        bytes_written += thread_data[t].bytes_written;
>>>> -
>>>> -    return bytes_written;
>>>> +    return rec->bytes_written + rec->thread_bytes_written;
>>>>    }
>>>>    static bool record__output_max_size_exceeded(struct record *rec)
>>>> @@ -255,10 +249,12 @@ static int record__write(struct record *rec,
>>>> struct mmap *map __maybe_unused,
>>>>            return -1;
>>>>        }
>>>> -    if (map && map->file)
>>>> +    if (map && map->file) {
>>>>            thread->bytes_written += size;
>>>> -    else
>>>> +        rec->thread_bytes_written += size;
>>>> +    } else {
>>>>            rec->bytes_written += size;
>>>> +    }
>>>>        if (record__output_max_size_exceeded(rec) && !done) {
>>>>            fprintf(stderr, "[ perf record: perf size limit reached (%"
>>>> PRIu64 " KB),"
>>>>
>>>
>>> .
> 
> .
>