1 files changed, 27 insertions, 3 deletions

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index b98bed3d8182..65b09a836cc3 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -1620,8 +1620,12 @@ static void rotate_ctx(struct perf_event_context *ctx)
 {
         raw_spin_lock(&ctx->lock);
 
-        /* Rotate the first entry last of non-pinned groups */
-        list_rotate_left(&ctx->flexible_groups);
+        /*
+         * Rotate the first entry last of non-pinned groups. Rotation might be
+         * disabled by the inheritance code.
+         */
+        if (!ctx->rotate_disable)
+                list_rotate_left(&ctx->flexible_groups);
 
         raw_spin_unlock(&ctx->lock);
 }
@@ -1773,7 +1777,13 @@ static u64 perf_event_read(struct perf_event *event)
                 unsigned long flags;
 
                 raw_spin_lock_irqsave(&ctx->lock, flags);
-                update_context_time(ctx);
+                /*
+                 * may read while context is not active
+                 * (e.g., thread is blocked), in that case
+                 * we cannot update context time
+                 */
+                if (ctx->is_active)
+                        update_context_time(ctx);
                 update_event_times(event);
                 raw_spin_unlock_irqrestore(&ctx->lock, flags);
         }
@@ -5616,6 +5626,7 @@ int perf_event_init_task(struct task_struct *child)
         struct perf_event *event;
         struct task_struct *parent = current;
         int inherited_all = 1;
+        unsigned long flags;
         int ret = 0;
 
         child->perf_event_ctxp = NULL;
@@ -5656,6 +5667,15 @@ int perf_event_init_task(struct task_struct *child)
                         break;
         }
 
+        /*
+         * We can't hold ctx->lock when iterating the ->flexible_group list due
+         * to allocations, but we need to prevent rotation because
+         * rotate_ctx() will change the list from interrupt context.
+         */
+        raw_spin_lock_irqsave(&parent_ctx->lock, flags);
+        parent_ctx->rotate_disable = 1;
+        raw_spin_unlock_irqrestore(&parent_ctx->lock, flags);
+
         list_for_each_entry(event, &parent_ctx->flexible_groups, group_entry) {
                 ret = inherit_task_group(event, parent, parent_ctx, child,
                                          &inherited_all);
@@ -5663,6 +5683,10 @@ int perf_event_init_task(struct task_struct *child)
                         break;
         }
 
+        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;
 
         if (child_ctx && inherited_all) {