linux-kernel - [PATCH 02/10] dmapool: cleanup integer types

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Message-ID: <81004e69-d91f-9fbb-2b94-217b48a064c3@cybernetics.com>
Date:   Tue, 31 May 2022 14:13:32 -0400
From:   Tony Battersby <tonyb@...ernetics.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     iommu@...ts.linux-foundation.org, kernel-team@...com,
        Matthew Wilcox <willy@...radead.org>,
        Keith Busch <kbusch@...nel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Robin Murphy <robin.murphy@....com>,
        Tony Lindgren <tony@...mide.com>
Subject: [PATCH 02/10] dmapool: cleanup integer types

To represent the size of a single allocation, dmapool currently uses
'unsigned int' in some places and 'size_t' in other places.  Standardize
on 'unsigned int' to reduce overhead, but use 'size_t' when counting all
the blocks in the entire pool.

Signed-off-by: Tony Battersby <tonyb@...ernetics.com>
---

This puts an upper bound on 'size' of INT_MAX to avoid overflowing the
following comparison in pool_initialise_page():

unsigned int offset = 0;
unsigned int next = offset + pool->size;
if (unlikely((next + pool->size) > ...

'boundary' is passed in as a size_t but gets stored as an unsigned int.
'boundary' values >= 'allocation' do not have any effect, so clipping
'boundary' to 'allocation' keeps it within the range of unsigned int
without affecting anything else.  A few lines above (not in the diff)
you can see that if 'boundary' is passed in as 0 then it is set to
'allocation', so it is nothing new.  For reference, here is the
relevant code after being patched:

	if (!boundary)
		boundary = allocation;
	else if ((boundary < size) || (boundary & (boundary - 1)))
		return NULL;

	boundary = min(boundary, allocation);

 mm/dmapool.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/mm/dmapool.c b/mm/dmapool.c
index 0f89de408cbe..d7b372248111 100644
--- a/mm/dmapool.c
+++ b/mm/dmapool.c
@@ -43,10 +43,10 @@
 struct dma_pool {		/* the pool */
 	struct list_head page_list;
 	spinlock_t lock;
-	size_t size;
+	unsigned int size;
 	struct device *dev;
-	size_t allocation;
-	size_t boundary;
+	unsigned int allocation;
+	unsigned int boundary;
 	char name[32];
 	struct list_head pools;
 };
@@ -80,7 +80,7 @@ static ssize_t pools_show(struct device *dev, struct device_attribute *attr, cha
 	mutex_lock(&pools_lock);
 	list_for_each_entry(pool, &dev->dma_pools, pools) {
 		unsigned pages = 0;
-		unsigned blocks = 0;
+		size_t blocks = 0;
 
 		spin_lock_irq(&pool->lock);
 		list_for_each_entry(page, &pool->page_list, page_list) {
@@ -90,9 +90,10 @@ static ssize_t pools_show(struct device *dev, struct device_attribute *attr, cha
 		spin_unlock_irq(&pool->lock);
 
 		/* per-pool info, no real statistics yet */
-		temp = scnprintf(next, size, "%-16s %4u %4zu %4zu %2u\n",
+		temp = scnprintf(next, size, "%-16s %4zu %4zu %4u %2u\n",
 				 pool->name, blocks,
-				 pages * (pool->allocation / pool->size),
+				 (size_t) pages *
+				 (pool->allocation / pool->size),
 				 pool->size, pages);
 		size -= temp;
 		next += temp;
@@ -139,7 +140,7 @@ struct dma_pool *dma_pool_create(const char *name, struct device *dev,
 	else if (align & (align - 1))
 		return NULL;
 
-	if (size == 0)
+	if (size == 0 || size > INT_MAX)
 		return NULL;
 	else if (size < 4)
 		size = 4;
@@ -152,6 +153,8 @@ struct dma_pool *dma_pool_create(const char *name, struct device *dev,
 	else if ((boundary < size) || (boundary & (boundary - 1)))
 		return NULL;
 
+	boundary = min(boundary, allocation);
+
 	retval = kmalloc(sizeof(*retval), GFP_KERNEL);
 	if (!retval)
 		return retval;
@@ -312,7 +315,7 @@ void *dma_pool_alloc(struct dma_pool *pool, gfp_t mem_flags,
 {
 	unsigned long flags;
 	struct dma_page *page;
-	size_t offset;
+	unsigned int offset;
 	void *retval;
 
 	might_alloc(mem_flags);
-- 
2.25.1