From 7a47627a88faa692baa3f0eef220ef2c36162363 Mon Sep 17 00:00:00 2001
From: Erik Gilling <konkers@android.com>
Date: Thu, 11 Oct 2012 12:35:22 -0700
Subject: [PATCH] sync: protect unlocked access to fence status
Fence status is checked outside of locks in both sync_fence_wait and
sync_fence_poll. This patch adds propper barrier protection in these
cases to avoid seeing stale status.
Change-Id: I9d8b6ce6accb415e797df58068a1ccd54e6be445
Signed-off-by: Erik Gilling <konkers@android.com>
---
drivers/base/sync.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)
diff --git a/drivers/base/sync.c b/drivers/base/sync.c
index 326e184a9bbd..4c5689ba56ce 100644
--- a/drivers/base/sync.c
+++ b/drivers/base/sync.c
@@ -556,6 +556,16 @@ int sync_fence_cancel_async(struct sync_fence *fence,
}
EXPORT_SYMBOL(sync_fence_cancel_async);
+static bool sync_fence_check(struct sync_fence *fence)
+{
+ /*
+ * Make sure that reads to fence->status are ordered with the
+ * wait queue event triggering
+ */
+ smp_rmb();
+ return fence->status != 0;
+}
+
int sync_fence_wait(struct sync_fence *fence, long timeout)
{
int err = 0;
@@ -563,7 +573,7 @@ int sync_fence_wait(struct sync_fence *fence, long timeout)
if (timeout > 0) {
timeout = msecs_to_jiffies(timeout);
err = wait_event_interruptible_timeout(fence->wq,
- fence->status != 0,
+ sync_fence_check(fence),
timeout);
} else if (timeout < 0) {
err = wait_event_interruptible(fence->wq, fence->status != 0);
@@ -627,6 +637,12 @@ static unsigned int sync_fence_poll(struct file *file, poll_table *wait)
poll_wait(file, &fence->wq, wait);
+ /*
+ * Make sure that reads to fence->status are ordered with the
+ * wait queue event triggering
+ */
+ smp_rmb();
+
if (fence->status == 1)
return POLLIN;
else if (fence->status < 0)
--
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