linux-kernel - [PATCH] fix order calculation in dma_mark_declared_memory

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Date:	Thu, 31 Jul 2008 16:46:42 +0100
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	<linux-kernel@...r.kernel.org>
Cc:	"Ingo Molnar" <mingo@...e.hu>, <dbaryshkov@...il.com>,
	<James.Bottomley@...senPartnership.com>
Subject: [PATCH] fix order calculation in
	dma_mark_declared_memory_occupied()

get_order() takes byte-sized input, not a page-granular one.

Irrespective of this fix I'm inclined to believe that this doesn't work
right anyway - bitmap_allocate_region() has an implicit assumption of
'pos' being suitable for 'order', which this function doesn't seem to
enforce (and since it's being called with a byte-granular value there's
no reason to believe that the callers would make sure device_addr is
passed accordingly - it's also not documented that way).

Signed-off-by: Jan Beulich <jbeulich@...ell.com>
Cc: James E.J. Bottomley <James.Bottomley@...senPartnership.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Dmitry Baryshkov <dbaryshkov@...il.com>

---
 kernel/dma-coherent.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- linux-2.6.27-rc1/kernel/dma-coherent.c	2008-07-31 17:08:36.000000000 +0200
+++ 2.6.27-rc1-dma-mark-declared/kernel/dma-coherent.c	2008-07-31 14:35:59.000000000 +0200
@@ -77,15 +77,14 @@ void *dma_mark_declared_memory_occupied(
 {
 	struct dma_coherent_mem *mem = dev->dma_mem;
 	int pos, err;
-	int pages = (size + (device_addr & ~PAGE_MASK) + PAGE_SIZE - 1);

-	pages >>= PAGE_SHIFT;
+	size += device_addr & ~PAGE_MASK;

 	if (!mem)
 		return ERR_PTR(-EINVAL);

 	pos = (device_addr - mem->device_base) >> PAGE_SHIFT;
-	err = bitmap_allocate_region(mem->bitmap, pos, get_order(pages));
+	err = bitmap_allocate_region(mem->bitmap, pos, get_order(size));
 	if (err != 0)
 		return ERR_PTR(err);
 	return mem->virt_base + (pos << PAGE_SHIFT);

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