perf_counter: Ammend cleanup in fork() fail

When fork() fails we cannot use perf_counter_exit_task() since that
assumes to operate on current. Write a new helper that cleans up
unused/clean contexts.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 43 insertions, 4 deletions

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 717bf3b59ba4..519a41bba249 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -579,6 +579,7 @@ extern void perf_counter_task_sched_out(struct task_struct *task,
 extern void perf_counter_task_tick(struct task_struct *task, int cpu);
 extern int perf_counter_init_task(struct task_struct *child);
 extern void perf_counter_exit_task(struct task_struct *child);
+extern void perf_counter_free_task(struct task_struct *task);
 extern void perf_counter_do_pending(void);
 extern void perf_counter_print_debug(void);
 extern void __perf_disable(void);
@@ -644,6 +645,7 @@ static inline void
 perf_counter_task_tick(struct task_struct *task, int cpu)               { }
 static inline int perf_counter_init_task(struct task_struct *child)     { return 0; }
 static inline void perf_counter_exit_task(struct task_struct *child)    { }
+static inline void perf_counter_free_task(struct task_struct *task)     { }
 static inline void perf_counter_do_pending(void)                        { }
 static inline void perf_counter_print_debug(void)                       { }
 static inline void perf_disable(void)                                   { }
diff --git a/kernel/fork.c b/kernel/fork.c
index c07c3335ceac..23bf757ed321 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1298,7 +1298,7 @@ bad_fork_cleanup_semundo:
 bad_fork_cleanup_audit:
         audit_free(p);
 bad_fork_cleanup_policy:
-        perf_counter_exit_task(p);
+        perf_counter_free_task(p);
 #ifdef CONFIG_NUMA
         mpol_put(p->mempolicy);
 bad_fork_cleanup_cgroup:
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 0c000d305e0e..79c3f26541d3 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -3538,8 +3538,7 @@ static void sync_child_counter(struct perf_counter *child_counter,
 }
 
 static void
-__perf_counter_exit_task(struct task_struct *child,
-                         struct perf_counter *child_counter,
+__perf_counter_exit_task(struct perf_counter *child_counter,
                          struct perf_counter_context *child_ctx)
 {
         struct perf_counter *parent_counter;
@@ -3605,7 +3604,7 @@ void perf_counter_exit_task(struct task_struct *child)
 again:
         list_for_each_entry_safe(child_counter, tmp, &child_ctx->counter_list,
                                  list_entry)
-                __perf_counter_exit_task(child, child_counter, child_ctx);
+                __perf_counter_exit_task(child_counter, child_ctx);
 
         /*
          * If the last counter was a group counter, it will have appended all
@@ -3621,6 +3620,44 @@ again:
 }
 
 /*
+ * free an unexposed, unused context as created by inheritance by
+ * init_task below, used by fork() in case of fail.
+ */
+void perf_counter_free_task(struct task_struct *task)
+{
+        struct perf_counter_context *ctx = task->perf_counter_ctxp;
+        struct perf_counter *counter, *tmp;
+
+        if (!ctx)
+                return;
+
+        mutex_lock(&ctx->mutex);
+again:
+        list_for_each_entry_safe(counter, tmp, &ctx->counter_list, list_entry) {
+                struct perf_counter *parent = counter->parent;
+
+                if (WARN_ON_ONCE(!parent))
+                        continue;
+
+                mutex_lock(&parent->child_mutex);
+                list_del_init(&counter->child_list);
+                mutex_unlock(&parent->child_mutex);
+
+                fput(parent->filp);
+
+                list_del_counter(counter, ctx);
+                free_counter(counter);
+        }
+
+        if (!list_empty(&ctx->counter_list))
+                goto again;
+
+        mutex_unlock(&ctx->mutex);
+
+        put_ctx(ctx);
+}
+
+/*
  * Initialize the perf_counter context in task_struct
  */
 int perf_counter_init_task(struct task_struct *child)