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Date: Sat, 28 Jan 2023 09:27:04 +0800
From: Yang Jihong <yangjihong1@...wei.com>
To: <acme@...nel.org>, <namhyung@...nel.org>,
<linux-perf-users@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC: <peterz@...radead.org>, <mingo@...hat.com>, <mark.rutland@....com>,
<alexander.shishkin@...ux.intel.com>, <jolsa@...nel.org>,
<jiwei.sun@...driver.com>
Subject: Re: [PATCH v3] perf record: Fix segfault with --overwrite and
--max-size
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@...ry=0x55f99755a200 <record>, event=event@...ry=0x55f9978da2e0, sample=sample@...ry=0x0, machine=machine@...ry=0x55f997893658) at builtin-record.c:618
> #4 0x000055f99716a883 in __perf_event__synthesize_id_index (tool=tool@...ry=0x55f99755a200 <record>, process=process@...ry=0x55f997002aa0 <process_synthesized_event>, evlist=0x55f9978928b0, machine=machine@...ry=0x55f997893658,
> from=from@...ry=0) at util/synthetic-events.c:1895
> #5 0x000055f99716a91f in perf_event__synthesize_id_index (tool=tool@...ry=0x55f99755a200 <record>, process=process@...ry=0x55f997002aa0 <process_synthesized_event>, evlist=<optimized out>, machine=machine@...ry=0x55f997893658)
> at util/synthetic-events.c:1905
> #6 0x000055f996fed4c3 in record__synthesize (tail=tail@...ry=true, rec=0x55f99755a200 <record>) at builtin-record.c:1997
> #7 0x000055f996fef7c8 in __cmd_record (argc=argc@...ry=2, argv=argv@...ry=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@...wei.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),"
>
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