1 files changed, 12 insertions, 11 deletions

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 05ebe841270b..84522c796987 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -2228,14 +2228,11 @@ find_get_context(struct pmu *pmu, struct task_struct *task, int cpu)
         unsigned long flags;
         int ctxn, err;
 
-        if (!task && cpu != -1) {
+        if (!task) {
                 /* Must be root to operate on a CPU event: */
                 if (perf_paranoid_cpu() && !capable(CAP_SYS_ADMIN))
                         return ERR_PTR(-EACCES);
 
-                if (cpu < 0 || cpu >= nr_cpumask_bits)
-                        return ERR_PTR(-EINVAL);
-
                 /*
                  * We could be clever and allow to attach a event to an
                  * offline CPU and activate it when the CPU comes up, but
@@ -5541,6 +5538,11 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
         struct hw_perf_event *hwc;
         long err;
 
+        if ((unsigned)cpu >= nr_cpu_ids) {
+                if (!task || cpu != -1)
+                        return ERR_PTR(-EINVAL);
+        }
+
         event = kzalloc(sizeof(*event), GFP_KERNEL);
         if (!event)
                 return ERR_PTR(-ENOMEM);
@@ -5589,7 +5591,7 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
 
         if (!overflow_handler && parent_event)
                 overflow_handler = parent_event->overflow_handler;
-        
+
         event->overflow_handler = overflow_handler;
 
         if (attr->disabled)
@@ -6494,7 +6496,6 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
 
         raw_spin_lock_irqsave(&parent_ctx->lock, flags);
         parent_ctx->rotate_disable = 0;
-        raw_spin_unlock_irqrestore(&parent_ctx->lock, flags);
 
         child_ctx = child->perf_event_ctxp[ctxn];
 
@@ -6502,12 +6503,11 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
                 /*
                  * Mark the child context as a clone of the parent
                  * context, or of whatever the parent is a clone of.
-                 * Note that if the parent is a clone, it could get
-                 * uncloned at any point, but that doesn't matter
-                 * because the list of events and the generation
-                 * count can't have changed since we took the mutex.
+                 *
+                 * Note that if the parent is a clone, the holding of
+                 * parent_ctx->lock avoids it from being uncloned.
                  */
-                cloned_ctx = rcu_dereference(parent_ctx->parent_ctx);
+                cloned_ctx = parent_ctx->parent_ctx;
                 if (cloned_ctx) {
                         child_ctx->parent_ctx = cloned_ctx;
                         child_ctx->parent_gen = parent_ctx->parent_gen;
@@ -6518,6 +6518,7 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
                 get_ctx(child_ctx->parent_ctx);
         }
 
+        raw_spin_unlock_irqrestore(&parent_ctx->lock, flags);
         mutex_unlock(&parent_ctx->mutex);
 
         perf_unpin_context(parent_ctx);