Messages in this thread Patch in this message | | | From | Kajol Jain <> | Subject | [PATCH] perf/core: Fix hung issue on perf stat command during cpu hotplug | Date | Thu, 27 Aug 2020 12:17:32 +0530 |
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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 <kjain@linux.ibm.com> Reported-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> Reviewed-by: Barret Rhoden <brho@google.com> Tested-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> --- kernel/events/core.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
Changelog: - Remove RFC tag - Resolve some nits issues like space after if and added -ENXIO in comment msg of function 'task_function_call' as suggested by Barret Rhoden.
Link to the RFC: https://lkml.org/lkml/2020/8/26/896
diff --git a/kernel/events/core.c b/kernel/events/core.c index 5bfe8e3c6e44..cef646084198 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -99,7 +99,7 @@ static void remote_function(void *data) * retry due to any failures in smp_call_function_single(), such as if the * task_cpu() goes offline concurrently. * - * returns @func return value or -ESRCH when the process isn't running + * returns @func return value or -ESRCH or -ENXIO when the process isn't running */ static int task_function_call(struct task_struct *p, remote_function_f func, void *info) @@ -115,7 +115,8 @@ 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) + ret = data.ret; if (ret != -EAGAIN) break; -- 2.26.2
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