linux-kernel - [PATCH] dma-mapping: remove an unnecessary NULL check

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Date:   Wed, 24 Apr 2019 17:24:37 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Christoph Hellwig <hch@....de>, Ian Abbott <abbotti@....co.uk>,
        Jiri Slaby <jslaby@...e.com>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        iommu@...ts.linux-foundation.org,
        "kernel-janitors@...r.kernel.org H Hartley Sweeten" 
        <hsweeten@...ionengravers.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] dma-mapping: remove an unnecessary NULL check

We already dereferenced "dev" when we called get_dma_ops() so this NULL
check is too late.  We're not supposed to pass NULL "dev" pointers to
dma_alloc_attrs().

Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
---
There are still at least two drivers which do pass a NULL unfortunately.

drivers/staging/comedi/drivers/comedi_isadma.c:195 comedi_isadma_alloc() error: NULL dereference inside function 'dma_alloc_coherent()'
drivers/staging/comedi/drivers/comedi_isadma.c:227 comedi_isadma_free() error: NULL dereference inside function 'dma_free_coherent()'
drivers/tty/synclink.c:3667 mgsl_alloc_buffer_list_memory() error: NULL dereference inside function 'dma_alloc_coherent()'
drivers/tty/synclink.c:3738 mgsl_free_buffer_list_memory() error: NULL dereference inside function 'dma_free_coherent()'
drivers/tty/synclink.c:3777 mgsl_alloc_frame_memory() error: NULL dereference inside function 'dma_alloc_coherent()'
drivers/tty/synclink.c:3811 mgsl_free_frame_memory() error: NULL dereference inside function 'dma_free_coherent()'

If I remember right there are one or two others which sometimes pass a
NULL, but it's harder to grep for those warnings.

 kernel/dma/mapping.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 685a53f2a793..f7afdadb6770 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -244,7 +244,7 @@ void *dma_alloc_attrs(struct device *dev, size_t size, dma_addr_t *dma_handle,
 	const struct dma_map_ops *ops = get_dma_ops(dev);
 	void *cpu_addr;
 
-	WARN_ON_ONCE(dev && !dev->coherent_dma_mask);
+	WARN_ON_ONCE(!dev->coherent_dma_mask);
 
 	if (dma_alloc_from_dev_coherent(dev, size, dma_handle, &cpu_addr))
 		return cpu_addr;
-- 
2.18.0