Merge branch 'perf-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'perf-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  perf: Fix the software context switch counter
  perf, x86: Fixup Kconfig deps
  x86, perf, nmi: Disable perf if counters are not accessible
  perf: Fix inherit vs. context rotation bug

1 files changed, 20 insertions, 4 deletions

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 671f6c8c8a3..eac7e336433 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -1287,8 +1287,6 @@ void __perf_event_task_sched_out(struct task_struct *task,
 {
         int ctxn;
 
-        perf_sw_event(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, 1, NULL, 0);
-
         for_each_task_context_nr(ctxn)
                 perf_event_context_sched_out(task, ctxn, next);
 }
@@ -1622,8 +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);
 }
@@ -6162,6 +6164,7 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
         struct perf_event *event;
         struct task_struct *parent = current;
         int inherited_all = 1;
+        unsigned long flags;
         int ret = 0;
 
         child->perf_event_ctxp[ctxn] = NULL;
@@ -6202,6 +6205,15 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
                         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, ctxn, &inherited_all);
@@ -6209,6 +6221,10 @@ int perf_event_init_context(struct task_struct *child, int ctxn)
                         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[ctxn];
 
         if (child_ctx && inherited_all) {