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Subject: Re: [PATCH v3] perf record: Fix segfault with --overwrite and
 --max-size
To:     <acme@kernel.org>, <namhyung@kernel.org>,
        <linux-perf-users@vger.kernel.org>, <linux-kernel@vger.kernel.org>
References: <20230113073803.102950-1-yangjihong1@huawei.com>
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        <alexander.shishkin@linux.intel.com>, <jolsa@kernel.org>,
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From:   Yang Jihong <yangjihong1@huawei.com>
Message-ID: <29a8e0bc-e90b-b371-962b-58a4b8c87f20@huawei.com>
Date:   Sat, 28 Jan 2023 09:27:04 +0800
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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>
> ---
> 
> 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),"
>