Commit-ID: 683ede43dd412c6cad0d23578a018409ac9c683e
Gitweb: http://git.kernel.org/tip/683ede43dd412c6cad0d23578a018409ac9c683e
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Mon, 5 May 2014 12:11:24 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 7 May 2014 13:44:19 +0200
perf: Rework free paths
Primarily make perf_event_release_kernel() into put_event(), this will
allow kernel space to create per-task inherited events, and is safer
in general.
Also, document the free_event() assumptions.
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Vince Weaver <vincent.weaver@xxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Link: http://lkml.kernel.org/n/tip-rk9pvr6e1d0559lxstltbztc@xxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/events/core.c | 66 +++++++++++++++++++++++++++++++---------------------
1 file changed, 40 insertions(+), 26 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 0de1997..83505a3 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3251,7 +3251,8 @@ static void __free_event(struct perf_event *event)
call_rcu(&event->rcu_head, free_event_rcu);
}
-static void free_event(struct perf_event *event)
+
+static void _free_event(struct perf_event *event)
{
irq_work_sync(&event->pending);
@@ -3279,42 +3280,31 @@ static void free_event(struct perf_event *event)
if (is_cgroup_event(event))
perf_detach_cgroup(event);
-
__free_event(event);
}
-int perf_event_release_kernel(struct perf_event *event)
+/*
+ * Used to free events which have a known refcount of 1, such as in error paths
+ * where the event isn't exposed yet and inherited events.
+ */
+static void free_event(struct perf_event *event)
{
- struct perf_event_context *ctx = event->ctx;
-
- WARN_ON_ONCE(ctx->parent_ctx);
- /*
- * There are two ways this annotation is useful:
- *
- * 1) there is a lock recursion from perf_event_exit_task
- * see the comment there.
- *
- * 2) there is a lock-inversion with mmap_sem through
- * perf_event_read_group(), which takes faults while
- * holding ctx->mutex, however this is called after
- * the last filedesc died, so there is no possibility
- * to trigger the AB-BA case.
- */
- mutex_lock_nested(&ctx->mutex, SINGLE_DEPTH_NESTING);
- perf_remove_from_context(event, true);
- mutex_unlock(&ctx->mutex);
-
- free_event(event);
+ if (WARN(atomic_long_cmpxchg(&event->refcount, 1, 0) != 1,
+ "unexpected event refcount: %ld; ptr=%p\n",
+ atomic_long_read(&event->refcount), event)) {
+ /* leak to avoid use-after-free */
+ return;
+ }
- return 0;
+ _free_event(event);
}
-EXPORT_SYMBOL_GPL(perf_event_release_kernel);
/*
* Called when the last reference to the file is gone.
*/
static void put_event(struct perf_event *event)
{
+ struct perf_event_context *ctx = event->ctx;
struct task_struct *owner;
if (!atomic_long_dec_and_test(&event->refcount))
@@ -3353,9 +3343,33 @@ static void put_event(struct perf_event *event)
put_task_struct(owner);
}
- perf_event_release_kernel(event);
+ WARN_ON_ONCE(ctx->parent_ctx);
+ /*
+ * There are two ways this annotation is useful:
+ *
+ * 1) there is a lock recursion from perf_event_exit_task
+ * see the comment there.
+ *
+ * 2) there is a lock-inversion with mmap_sem through
+ * perf_event_read_group(), which takes faults while
+ * holding ctx->mutex, however this is called after
+ * the last filedesc died, so there is no possibility
+ * to trigger the AB-BA case.
+ */
+ mutex_lock_nested(&ctx->mutex, SINGLE_DEPTH_NESTING);
+ perf_remove_from_context(event, true);
+ mutex_unlock(&ctx->mutex);
+
+ _free_event(event);
}
+int perf_event_release_kernel(struct perf_event *event)
+{
+ put_event(event);
+ return 0;
+}
+EXPORT_SYMBOL_GPL(perf_event_release_kernel);
+
static int perf_release(struct inode *inode, struct file *file)
{
put_event(file->private_data);
--
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