Re: linux-next: build failure after merge of the net-next tree

David Miller
2015-08-24T03:33:25Z

From: Stephen Rothwell <sfr@canb.auug.org.au>
Date: Mon, 24 Aug 2015 13:21:11 +1000

> After merging the net-next tree, today's linux-next build (arm
> multi_v7_defconfig) failed like this:

Fixed by:

====================
[PATCH] route: fix breakage after moving lwtunnel state

__recnt and related fields need to be in its own cacheline for performance
reasons. Commit 61adedf3e3f1 ("route: move lwtunnel state to dst_entry")
broke that on 32bit archs, causing BUILD_BUG_ON in dst_hold to be triggered.

This patch fixes the breakage by moving the lwtunnel state to the end of
dst_entry on 32bit archs. Unfortunately, this makes it share the cacheline
with __refcnt and may affect performance, thus further patches may be
needed.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Fixes: 61adedf3e3f1 ("route: move lwtunnel state to dst_entry")
Signed-off-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
include/net/dst.h | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/include/net/dst.h b/include/net/dst.h
index 0a9a723..ef8f1d4 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -44,7 +44,6 @@ struct dst_entry {
#else
void *__pad1;
#endif
- struct lwtunnel_state *lwtstate;
int (*input)(struct sk_buff *);
int (*output)(struct sock *sk, struct sk_buff *skb);

@@ -85,11 +84,12 @@ struct dst_entry {
__u32 __pad2;
#endif

+#ifdef CONFIG_64BIT
+ struct lwtunnel_state *lwtstate;
/*
* Align __refcnt to a 64 bytes alignment
* (L1_CACHE_SIZE would be too much)
*/
-#ifdef CONFIG_64BIT
long __pad_to_align_refcnt[1];
#endif
/*
@@ -99,6 +99,9 @@ struct dst_entry {
atomic_t __refcnt; /* client references */
int __use;
unsigned long lastuse;
+#ifndef CONFIG_64BIT
+ struct lwtunnel_state *lwtstate;
+#endif
union {
struct dst_entry *next;
struct rtable __rcu *rt_next;
--
2.1.0