linux-kernel - [PATCH 3.17 08/47] xen-netfront: Remove BUGs on paged skb data which crosses a page boundary

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Message-Id: <20141214201818.816491840@linuxfoundation.org>
Date:	Sun, 14 Dec 2014 12:20:43 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Seth Forshee <seth.forshee@...onical.com>,
	David Vrabel <david.vrabel@...rix.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [PATCH 3.17 08/47] xen-netfront: Remove BUGs on paged skb data which crosses a page boundary

3.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Seth Forshee <seth.forshee@...onical.com>

commit 8d609725d4357f499e2103e46011308b32f53513 upstream.

These BUGs can be erroneously triggered by frags which refer to
tail pages within a compound page. The data in these pages may
overrun the hardware page while still being contained within the
compound page, but since compound_order() evaluates to 0 for tail
pages the assertion fails. The code already iterates through
subsequent pages correctly in this scenario, so the BUGs are
unnecessary and can be removed.

Fixes: f36c374782e4 ("xen/netfront: handle compound page fragments on transmit")
Signed-off-by: Seth Forshee <seth.forshee@...onical.com>
Reviewed-by: David Vrabel <david.vrabel@...rix.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/net/xen-netfront.c |    5 -----
 1 file changed, 5 deletions(-)

--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -496,9 +496,6 @@ static void xennet_make_frags(struct sk_
 		len = skb_frag_size(frag);
 		offset = frag->page_offset;

-		/* Data must not cross a page boundary. */
-		BUG_ON(len + offset > PAGE_SIZE<<compound_order(page));
-
 		/* Skip unused frames from start of page */
 		page += offset >> PAGE_SHIFT;
 		offset &= ~PAGE_MASK;
@@ -506,8 +503,6 @@ static void xennet_make_frags(struct sk_
 		while (len > 0) {
 			unsigned long bytes;

-			BUG_ON(offset >= PAGE_SIZE);
-
 			bytes = PAGE_SIZE - offset;
 			if (bytes > len)
 				bytes = len;

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