From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Robert Mader <robert.mader@collabora.com>,
	Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>,
	Vivek Kasireddy <vivek.kasireddy@intel.com>
Subject: [PATCH 5.15 269/272] udmabuf: Ensure to perform cache synchronisation in begin_cpu_udmabuf()
Date: Thu, 20 Aug 2026 16:57:33 +0200
Message-ID: <20260820145239.704918624@linuxfoundation.org>
In-Reply-To: <20260820145231.229664293@linuxfoundation.org>
References: <20260820145231.229664293@linuxfoundation.org>
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5.15-stable review patch.  If anyone has any objections, please let me know.

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

From: Robert Mader <robert.mader@collabora.com>

commit 1d0e25c1ddf2063c499264fb2ba0fa6a3e4f8a00 upstream.

The message of commit 504e2b4ab97a ("dma-buf/udmabuf: skip redundant cpu sync to
fix cacheline EEXIST warning") says:

> The CPU sync at map/unmap time is also redundant for udmabuf:
> begin_cpu_udmabuf() and end_cpu_udmabuf() already perform explicit
> cache synchronization via dma_sync_sgtable_for_cpu/device() when CPU
> access is requested through the dma-buf interface.

This, however, does not apply to the first time begin_cpu_udmabuf() is
called on an udmabuf, in which case the implementation previously relied on
get_sg_table() to perform the cache synchronisation.

Ensure to call dma_sync_sgtable_for_cpu() in that case as well.

Fixes: 504e2b4ab97a ("dma-buf/udmabuf: skip redundant cpu sync to fix cacheline EEXIST warning")
Signed-off-by: Robert Mader <robert.mader@collabora.com>
Reviewed-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Link: https://patch.msgid.link/20260627105725.9083-1-robert.mader@collabora.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/dma-buf/udmabuf.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -127,21 +127,22 @@ static int begin_cpu_udmabuf(struct dma_
 {
 	struct udmabuf *ubuf = buf->priv;
 	struct device *dev = ubuf->device->this_device;
-	int ret = 0;
 
 	if (!ubuf->sg) {
 		ubuf->sg = get_sg_table(dev, buf, direction);
 		if (IS_ERR(ubuf->sg)) {
+			int ret;
+
 			ret = PTR_ERR(ubuf->sg);
 			ubuf->sg = NULL;
+			return ret;
 		} else {
 			ubuf->sg_dir = direction;
 		}
-	} else {
-		dma_sync_sgtable_for_cpu(dev, ubuf->sg, direction);
 	}
 
-	return ret;
+	dma_sync_sgtable_for_cpu(dev, ubuf->sg, direction);
+	return 0;
 }
 
 static int end_cpu_udmabuf(struct dma_buf *buf,