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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Andrew Bresticker <abrestic@chromium.org>,
        Dmitry Torokhov <dtor@chromium.org>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.4 046/131] android: unconditionally remove callbacks in sync_fence_free()
Date:   Mon,  1 Apr 2019 19:01:56 +0200
Message-Id: <20190401170056.159747084@linuxfoundation.org>
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4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit 699f685569434510d944e419f4048c4e3ba8d631 ]

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@chromium.org>
Signed-off-by: Dmitry Torokhov <dtor@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.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 f83e00c78051..50a9945da27e 100644
--- a/drivers/staging/android/sync.c
+++ b/drivers/staging/android/sync.c
@@ -519,12 +519,10 @@ 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);
 	}
 
-- 
2.19.1