From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnaldo Carvalho de Melo Subject: Re: [RFC] perf/core: Fixes hung issue on perf stat command during cpu hotplug Date: Wed, 26 Aug 2020 10:21:07 -0300 Message-ID: <20200826132107.GH1059382@kernel.org> References: <20200826093236.446024-1-kjain@linux.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20200826093236.446024-1-kjain@linux.ibm.com> Sender: linux-kernel-owner@vger.kernel.org To: Kajol Jain 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 List-Id: linux-perf-users.vger.kernel.org Em Wed, Aug 26, 2020 at 03:02:36PM +0530, Kajol Jain escreveu: > 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 ) Peter, this is kernel stuff, can you take a look? - Arnaldo > 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 > -- - Arnaldo