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Message-ID: <20140418165958.GQ13658@twins.programming.kicks-ass.net>
Date: Fri, 18 Apr 2014 18:59:58 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Vince Weaver <vincent.weaver@...ne.edu>
Cc: Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
Thomas Gleixner <tglx@...utronix.de>,
Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [perf] more perf_fuzzer memory corruption
On Fri, Apr 18, 2014 at 05:23:14PM +0200, Peter Zijlstra wrote:
> OK, that's a good clue. That looks like we're freeing events that still
> are on the owner list, which would indicate we're freeing events that
> have a refcount.
>
> I added a WARN in free_event() to check the refcount, along with a
> number of false positives (through the perf_event_open() fail path) I do
> appear to be getting actual fails here.
>
> At least I can 'reproduce' this. Earlier attempts, even based on your
> .config only got me very mysterious lockups -- I suspect the corruption
> happens on a slightly different spot or so and completely messes up the
> machine.
The below should have only made the false positives go away, but my
machine has magically stopped going all funny on me. Could you give it a
go?
---
kernel/events/core.c | 73 +++++++++++++++++++++++++++++++---------------------
1 file changed, 43 insertions(+), 30 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index f83a71a3e46d..f9d7b859395e 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3231,8 +3231,11 @@ 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)
{
+ WARN_ON(atomic_long_read(&event->refcount));
+
irq_work_sync(&event->pending);
unaccount_event(event);
@@ -3259,45 +3262,28 @@ 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)
-{
- 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);
- raw_spin_lock_irq(&ctx->lock);
- perf_group_detach(event);
- raw_spin_unlock_irq(&ctx->lock);
- perf_remove_from_context(event);
- mutex_unlock(&ctx->mutex);
-
- free_event(event);
+static void put_event(struct perf_event *event);
- return 0;
+static void free_event(struct perf_event *event)
+{
+ if (unlikely(atomic_long_cmpxchg(&event->refcount, 1, 0) != 1)) {
+ WARN(1, "unexpected event refcount: %ld\n",
+ atomic_long_read(&event->refcount));
+ put_event(event);
+ return;
+ }
+ _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))
@@ -3336,9 +3322,36 @@ 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);
+ raw_spin_lock_irq(&ctx->lock);
+ perf_group_detach(event);
+ raw_spin_unlock_irq(&ctx->lock);
+ perf_remove_from_context(event);
+ 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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