linux-kernel - [PATCH] android: unconditionally remove callbacks in sync_fence

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Message-ID: <20151215013408.GA28746@dtor-ws>
Date:	Mon, 14 Dec 2015 17:34:08 -0800
From:	Dmitry Torokhov <dtor@...omium.org>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Arve Hjønnevåg <arve@...roid.com>,
	Riley Andrews <riandrews@...roid.com>,
	Andrew Bresticker <abrestic@...omium.org>,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: [PATCH] android: unconditionally remove callbacks in
 sync_fence_free()

Using fence->status to determine whether or not there are callbacks
remaining on the sync_fence is racy since fence->status may have been
decremented to 0 on another CPU before fence_check_cb_func() has
completed.  By unconditionally calling fence_remove_callback() for each
fence in the sync_fence, we guarantee that each callback has either
completed (since fence_remove_callback() grabs the fence lock) or been
removed.

Signed-off-by: Andrew Bresticker <abrestic@...omium.org>
Signed-off-by: Dmitry Torokhov <dtor@...omium.org>
---
 drivers/staging/android/sync.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
index f8566c1..f3814a8 100644
--- a/drivers/staging/android/sync.c
+++ b/drivers/staging/android/sync.c
@@ -527,12 +527,10 @@ static const struct fence_ops android_fence_ops = {
 static void sync_fence_free(struct kref *kref)
 {
 	struct sync_fence *fence = container_of(kref, struct sync_fence, kref);
-	int i, status = atomic_read(&fence->status);
+	int i;
 
 	for (i = 0; i < fence->num_fences; ++i) {
-		if (status)
-			fence_remove_callback(fence->cbs[i].sync_pt,
-					      &fence->cbs[i].cb);
+		fence_remove_callback(fence->cbs[i].sync_pt, &fence->cbs[i].cb);
 		fence_put(fence->cbs[i].sync_pt);
 	}
 
-- 
2.6.0.rc2.230.g3dd15c0


-- 
Dmitry
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