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Subject[PATCH V6 02/13] perf: Avoid race between cpu hotplug and installing event
Date
From: "Yan, Zheng" <zheng.z.yan@intel.com>

perf_event_open requires the cpu on which to install event is online,
but the cpu can go offline after perf_event_open checks that. Add
get_online_cpus()/put_online_cpus() pair to avoid the race.

Signed-off-by: Zheng Yan <zheng.z.yan@intel.com>
---
kernel/events/core.c | 5 +++++
1 files changed, 5 insertions(+), 0 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index f85c015..d71a2d6 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6248,6 +6248,8 @@ SYSCALL_DEFINE5(perf_event_open,
}
}

+ get_online_cpus();
+
event = perf_event_alloc(&attr, cpu, task, group_leader, NULL,
NULL, NULL);
if (IS_ERR(event)) {
@@ -6387,6 +6389,8 @@ SYSCALL_DEFINE5(perf_event_open,
perf_unpin_context(ctx);
mutex_unlock(&ctx->mutex);

+ put_online_cpus();
+
event->owner = current;

mutex_lock(&current->perf_event_mutex);
@@ -6415,6 +6419,7 @@ err_context:
err_alloc:
free_event(event);
err_task:
+ put_online_cpus();
if (task)
put_task_struct(task);
err_group_fd:
--
1.7.6.5


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