linux-kernel - [PATCH v2 2/2] drivers: dma-coherent: Move spinlock in dma_alloc_from

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Date:   Wed, 28 Sep 2016 08:51:57 +0100
From:   Mark Craske <Mark_Craske@...tor.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     <linux-kernel@...r.kernel.org>,
        "George G. Davis" <George_Davis@...tor.com>,
        Jiada Wang <Jiada_Wang@...tor.com>
Subject: [PATCH v2 2/2] drivers: dma-coherent: Move spinlock in dma_alloc_from_coherent()

From: Bastian Hecht <bhecht@...adit-jv.com>

We don't need to hold the spinlock while zeroing the allocated memory.
In case we handle big buffers this is a severe issue as other CPUs might
be spinning half a second or longer.

Signed-off-by: Bastian Hecht <bhecht@...adit-jv.com>
Signed-off-by: George G. Davis <george_davis@...tor.com>
Signed-off-by: Mark Craske <Mark_Craske@...tor.com>
---
 drivers/base/dma-coherent.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/base/dma-coherent.c b/drivers/base/dma-coherent.c
index 2789f7a..640a7e6 100644
--- a/drivers/base/dma-coherent.c
+++ b/drivers/base/dma-coherent.c
@@ -165,6 +165,7 @@ int dma_alloc_from_coherent(struct device *dev, ssize_t size,
 	int order = get_order(size);
 	unsigned long flags;
 	int pageno;
+	int dma_memory_map;
 
 	if (!dev)
 		return 0;
@@ -187,11 +188,12 @@ int dma_alloc_from_coherent(struct device *dev, ssize_t size,
 	 */
 	*dma_handle = mem->device_base + (pageno << PAGE_SHIFT);
 	*ret = mem->virt_base + (pageno << PAGE_SHIFT);
-	if (mem->flags & DMA_MEMORY_MAP)
+	dma_memory_map = (mem->flags & DMA_MEMORY_MAP);
+	spin_unlock_irqrestore(&mem->spinlock, flags);
+	if (dma_memory_map)
 		memset(*ret, 0, size);
 	else
 		memset_io(*ret, 0, size);
-	spin_unlock_irqrestore(&mem->spinlock, flags);
 
 	return 1;
 
-- 
1.7.9.5