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Thu, 27 Aug 2020 05:47:45 +0000 (GMT) Received: from linux.vnet.ibm.com (unknown [9.126.150.29]) by d06av21.portsmouth.uk.ibm.com (Postfix) with SMTP id 0EF8152050; Thu, 27 Aug 2020 05:47:42 +0000 (GMT) Date: Thu, 27 Aug 2020 11:17:42 +0530 From: Srikar Dronamraju To: Kajol Jain Cc: acme@kernel.org, peterz@infradead.org, jolsa@redhat.com, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, maddy@linux.ibm.com, mingo@redhat.com, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, namhyung@kernel.org, daniel@iogearbox.net, brho@google.com Subject: Re: [RFC v2] perf/core: Fixes hung issue on perf stat command during cpu hotplug Message-ID: <20200827054742.GA5431@linux.vnet.ibm.com> Reply-To: Srikar Dronamraju References: <20200826145411.489169-1-kjain@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20200826145411.489169-1-kjain@linux.ibm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235,18.0.687 definitions=2020-08-27_01:2020-08-26,2020-08-27 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxscore=0 spamscore=0 phishscore=0 clxscore=1011 malwarescore=0 impostorscore=0 lowpriorityscore=0 bulkscore=0 mlxlogscore=999 adultscore=0 suspectscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2008270041 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Kajol Jain [2020-08-26 20:24:11]: > Commit 2ed6edd33a21 ("perf: Add cond_resched() to task_function_call()") > added assignment of ret value as -EAGAIN in case function > call to 'smp_call_function_single' fails. > For non-zero ret value, it did > 'ret = !ret ? data.ret : -EAGAIN;', which always > assign -EAGAIN to ret and make second if condition useless. > > In scenarios like when executing a perf stat with --per-thread option, and > if any of the monitoring cpu goes offline, the 'smp_call_function_single' > function could return -ENXIO, and with the above check, > task_function_call hung and increases CPU > usage (because of repeated 'smp_call_function_single()') > > Recration scenario: > # perf stat -a --per-thread && (offline a CPU ) > > Patch here removes the tertiary condition added as part of that > commit and added a check for NULL and -EAGAIN. > > Fixes: 2ed6edd33a21("perf: Add cond_resched() to task_function_call()") > Signed-off-by: Kajol Jain > Reported-by: Srikar Dronamraju Tested-by: Srikar Dronamraju -- Thanks and Regards Srikar Dronamraju