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Wed, 26 Aug 2020 09:32:58 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 1738A4C040; Wed, 26 Aug 2020 09:32:55 +0000 (GMT) Received: from localhost.localdomain.com (unknown [9.77.206.242]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 26 Aug 2020 09:32:54 +0000 (GMT) From: Kajol Jain To: acme@kernel.org Cc: jolsa@redhat.com, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, maddy@linux.ibm.com, peterz@infradead.org, mingo@redhat.com, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, namhyung@kernel.org, daniel@iogearbox.net, brho@google.com, srikar@linux.vnet.ibm.com, kjain@linux.ibm.com Subject: [RFC] perf/core: Fixes hung issue on perf stat command during cpu hotplug Date: Wed, 26 Aug 2020 15:02:36 +0530 Message-Id: <20200826093236.446024-1-kjain@linux.ibm.com> X-Mailer: git-send-email 2.26.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235,18.0.687 definitions=2020-08-26_06:2020-08-25,2020-08-26 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=1 mlxlogscore=999 mlxscore=0 malwarescore=0 priorityscore=1501 lowpriorityscore=0 spamscore=0 phishscore=0 bulkscore=0 adultscore=0 clxscore=1011 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2008260072 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- kernel/events/core.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 5bfe8e3c6e44..330c53f7df9c 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -115,9 +115,9 @@ task_function_call(struct task_struct *p, remote_function_f func, void *info) for (;;) { ret = smp_call_function_single(task_cpu(p), remote_function, &data, 1); - ret = !ret ? data.ret : -EAGAIN; - - if (ret != -EAGAIN) + if (!ret) + ret = data.ret; + else if (ret != -EAGAIN) break; cond_resched(); -- 2.26.2