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Fix and allocate less memory for ->priv'less netdevices

PATCH In review Alexey Dobriyan 2 participants 2 messages Apr 18, 2008

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Networking Network drivers
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Alexey Dobriyan

author
#0 lore raw

PATCH 1/1 Fix and allocate less memory for ->priv'less netdevices

This patch effectively reverts commit d0498d9ae1a5cebac363e38907266d5cd2eedf89 aka "[NET]: Do not allocate unneeded memory for dev->priv alignment." It was found to be buggy because of final unconditional += NETDEV_ALIGN_CONST removal.

For example, for sizeof(struct net_device) being 2048 bytes, "alloc_size" was also 2048 bytes, but allocator with debugging options turned on started giving out !32-byte aligned memory resulting in redzones overwrites.

Patch does small optimization in ->priv'less case: bumping size to next 32-byte boundary was always done to ensure ->priv will also be aligned. But, no ->priv, no need to do that.

Signed-off-by Alexey Dobriyan <[email protected]>

---

 net/core/dev.c |   15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)
net/core/dev.c +9 -6
@@ -3996,12 +3996,15 @@ struct net_device *alloc_netdev_mq(int sizeof_priv, const char *name,
 
 	BUG_ON(strlen(name) >= sizeof(dev->name));
 
-	/* ensure 32-byte alignment of both the device and private area */
-	alloc_size = (sizeof(*dev) + NETDEV_ALIGN_CONST +
-		     (sizeof(struct net_device_subqueue) * (queue_count - 1))) &
-		     ~NETDEV_ALIGN_CONST;
-	if (sizeof_priv)
-		alloc_size += sizeof_priv + NETDEV_ALIGN_CONST;
+	alloc_size = sizeof(struct net_device) +
+		     sizeof(struct net_device_subqueue) * (queue_count - 1);
+	if (sizeof_priv) {
+		/* ensure 32-byte alignment of private area */
+		alloc_size = (alloc_size + NETDEV_ALIGN_CONST) & ~NETDEV_ALIGN_CONST;
+		alloc_size += sizeof_priv;
+	}
+	/* ensure 32-byte alignment of whole construct */
+	alloc_size += NETDEV_ALIGN_CONST;
 
 	p = kzalloc(alloc_size, GFP_KERNEL);
 	if (!p) {
maintainer
#1 lore raw

From: Alexey Dobriyan <[email protected]>
Date: Fri, 18 Apr 2008 19:10:29 +0400

Quoted 9 lines

This patch effectively reverts commit d0498d9ae1a5cebac363e38907266d5cd2eedf89 aka "[NET]: Do not allocate unneeded memory for dev->priv alignment." It was found to be buggy because of final unconditional += NETDEV_ALIGN_CONST removal.

For example, for sizeof(struct net_device) being 2048 bytes, "alloc_size" was also 2048 bytes, but allocator with debugging options turned on started giving out !32-byte aligned memory resulting in redzones overwrites.

Quoted 5 lines

Patch does small optimization in ->priv'less case: bumping size to next 32-byte boundary was always done to ensure ->priv will also be aligned. But, no ->priv, no need to do that.

Signed-off-by Alexey Dobriyan <[email protected]>

Thanks for finding and fixing this regression.

Patch applied.