From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-110.freemail.mail.aliyun.com (out30-110.freemail.mail.aliyun.com [115.124.30.110]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EC47333507B; Wed, 29 Oct 2025 12:55:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.110 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761742527; cv=none; b=cUzjCDZz/WuXbj/Qiisp7+SR0t7+34H6q0lOzXHnSjaBA90qlWEf+dKOwx9pfY90BEWkZyOgvPx81Zx3AO/+xaBqgU2BeNF9nI2PHe48Klie4hBB6XN6R26PnKVvGxIzh2v/dz1esJOujGcvxIkMc+EB3ZWarxdEMij04/v8Y3Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761742527; c=relaxed/simple; bh=0wMW0XC224Kej5/7Y/10VzAOIoK/Gr9bBang0zCkkec=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=T4bY+lSVbxM65yT2xAuzqMRgeM8p6rGBY5nCuDg+qUf/AEOem63Ca4oE6OVu50GjphiOsAZL//WlIgURp/a0a87KEc8FPX04go6oIroxussfVNY5WCs6b+pKyUCam8QnQ/HrutoZmKJwt/zN4fq05AqTiEw+pN2ctXqPrm7UN+g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=EpvyDtnD; arc=none smtp.client-ip=115.124.30.110 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="EpvyDtnD" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1761742520; h=Message-ID:Date:MIME-Version:Subject:From:To:Content-Type; bh=1/s8TOdfgqqMhs6MPkKtJvuM4gO1U3iasXipTZ9JtZQ=; b=EpvyDtnDaPezKIVx6Xq+/nz15ofVNiB9hS5v2gD51IH2AIe1VbxozYCjthGjchjAPSJFCtkyQgrsaoABfiMgdBP+04T0gK2i6072iYq/0JBVP+L/IISKd5XsKnzU9Pt+vWOk8ifbxhBl/YsH/e72mzN4Sgp+LipR7LpMYUCSJ4s= Received: from 30.246.176.102(mailfrom:xueshuai@linux.alibaba.com fp:SMTPD_---0WrG16KC_1761742518 cluster:ay36) by smtp.aliyun-inc.com; Wed, 29 Oct 2025 20:55:19 +0800 Message-ID: Date: Wed, 29 Oct 2025 20:55:14 +0800 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] perf record: skip synthesize event when open evsel failed From: Shuai Xue To: Ian Rogers Cc: alexander.shishkin@linux.intel.com, peterz@infradead.org, james.clark@arm.com, leo.yan@linaro.org, mingo@redhat.com, baolin.wang@linux.alibaba.com, acme@kernel.org, mark.rutland@arm.com, jolsa@kernel.org, namhyung@kernel.org, adrian.hunter@intel.com, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, nathan@kernel.org, bpf@vger.kernel.org References: <20251023015043.38868-1-xueshuai@linux.alibaba.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 在 2025/10/24 10:45, Shuai Xue 写道: > > > 在 2025/10/24 00:08, Ian Rogers 写道: >> On Wed, Oct 22, 2025 at 6:50 PM Shuai Xue wrote: >>> >>> When using perf record with the `--overwrite` option, a segmentation fault >>> occurs if an event fails to open. For example: >>> >>>    perf record -e cycles-ct -F 1000 -a --overwrite >>>    Error: >>>    cycles-ct:H: PMU Hardware doesn't support sampling/overflow-interrupts. Try 'perf stat' >>>    perf: Segmentation fault >>>        #0 0x6466b6 in dump_stack debug.c:366 >>>        #1 0x646729 in sighandler_dump_stack debug.c:378 >>>        #2 0x453fd1 in sigsegv_handler builtin-record.c:722 >>>        #3 0x7f8454e65090 in __restore_rt libc-2.32.so[54090] >>>        #4 0x6c5671 in __perf_event__synthesize_id_index synthetic-events.c:1862 >>>        #5 0x6c5ac0 in perf_event__synthesize_id_index synthetic-events.c:1943 >>>        #6 0x458090 in record__synthesize builtin-record.c:2075 >>>        #7 0x45a85a in __cmd_record builtin-record.c:2888 >>>        #8 0x45deb6 in cmd_record builtin-record.c:4374 >>>        #9 0x4e5e33 in run_builtin perf.c:349 >>>        #10 0x4e60bf in handle_internal_command perf.c:401 >>>        #11 0x4e6215 in run_argv perf.c:448 >>>        #12 0x4e653a in main perf.c:555 >>>        #13 0x7f8454e4fa72 in __libc_start_main libc-2.32.so[3ea72] >>>        #14 0x43a3ee in _start ??:0 >>> >>> The --overwrite option implies --tail-synthesize, which collects non-sample >>> events reflecting the system status when recording finishes. However, when >>> evsel opening fails (e.g., unsupported event 'cycles-ct'), session->evlist >>> is not initialized and remains NULL. The code unconditionally calls >>> record__synthesize() in the error path, which iterates through the NULL >>> evlist pointer and causes a segfault. >>> >>> To fix it, move the record__synthesize() call inside the error check block, so >>> it's only called when there was no error during recording, ensuring that evlist >>> is properly initialized. >>> >>> Fixes: 4ea648aec019 ("perf record: Add --tail-synthesize option") >>> Signed-off-by: Shuai Xue >> >> This looks great! I wonder if we can add a test, perhaps here: >> https://web.git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/tests/shell/record.sh?h=perf-tools-next#n435 >> something like: >> ``` >> $ perf record -e foobar -F 1000 -a --overwrite -o /dev/null -- sleep 0.1 >> ``` >> in a new test subsection for test_overwrite? foobar would be an event >> that we could assume isn't present. Could you help with a test >> covering the problems you've uncovered and perhaps related flags? >> > > Hi, Ian, > > Good suggestion, I'd like to add a test. But foobar may not a good case. > > Regarding your example: > >   perf record -e foobar -a --overwrite -o /dev/null -- sleep 0.1 >   event syntax error: 'foobar' >                        \___ Bad event name > >   Unable to find event on a PMU of 'foobar' >   Run 'perf list' for a list of valid events > >    Usage: perf record [] [] >       or: perf record [] -- [] > >       -e, --event    event selector. use 'perf list' to list available events > > > The issue with using foobar is that it's an invalid event name, and the > perf parser will reject it much earlier. This means the test would exit > before reaching the part of the code path we want to verify (where > record__synthesize() could be called). > > A potential alternative could be testing an error case such as EACCES: > >   perf record -e cycles -C 0 --overwrite -o /dev/null -- sleep 0.1 > > This could reproduce the scenario of a failure when attempting to access > a valid event, such as due to permission restrictions. However, the > limitation here is that users may override > /proc/sys/kernel/perf_event_paranoid, which affects whether or not this > test would succeed in triggering an EACCES error. > > > If you have any other suggestions or ideas for a better way to simulate > this situation, I'd love to hear them. > > Thanks. > Shuai Hi, Ian, Gentle ping. Thanks. Shuai