From dedf6341b7db69ced872963e0c28f333808b9a50 Mon Sep 17 00:00:00 2001
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Fri, 15 Jan 2016 16:33:34 +0100
Subject: [PATCH 268/365] net/core: protect users of napi_alloc_cache against
 reentrance

On -RT the code running in BH can not be moved to another CPU so CPU
local variable remain local. However the code can be preempted
and another task may enter BH accessing the same CPU using the same
napi_alloc_cache variable.
This patch ensures that each user of napi_alloc_cache uses a local lock.

Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 net/core/skbuff.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 9d20d9a5df1e..d76b2d7db8fe 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -353,6 +353,7 @@ EXPORT_SYMBOL(build_skb);
 static DEFINE_PER_CPU(struct page_frag_cache, netdev_alloc_cache);
 static DEFINE_PER_CPU(struct page_frag_cache, napi_alloc_cache);
 static DEFINE_LOCAL_IRQ_LOCK(netdev_alloc_lock);
+static DEFINE_LOCAL_IRQ_LOCK(napi_alloc_cache_lock);
 
 static void *__netdev_alloc_frag(unsigned int fragsz, gfp_t gfp_mask)
 {
@@ -382,9 +383,13 @@ EXPORT_SYMBOL(netdev_alloc_frag);
 
 static void *__napi_alloc_frag(unsigned int fragsz, gfp_t gfp_mask)
 {
-	struct page_frag_cache *nc = this_cpu_ptr(&napi_alloc_cache);
+	struct page_frag_cache *nc;
+	void *data;
 
-	return __alloc_page_frag(nc, fragsz, gfp_mask);
+	nc = &get_locked_var(napi_alloc_cache_lock, napi_alloc_cache);
+	data = __alloc_page_frag(nc, fragsz, gfp_mask);
+	put_locked_var(napi_alloc_cache_lock, napi_alloc_cache);
+	return data;
 }
 
 void *napi_alloc_frag(unsigned int fragsz)
@@ -478,9 +483,10 @@ EXPORT_SYMBOL(__netdev_alloc_skb);
 struct sk_buff *__napi_alloc_skb(struct napi_struct *napi, unsigned int len,
 				 gfp_t gfp_mask)
 {
-	struct page_frag_cache *nc = this_cpu_ptr(&napi_alloc_cache);
+	struct page_frag_cache *nc;
 	struct sk_buff *skb;
 	void *data;
+	bool pfmemalloc;
 
 	len += NET_SKB_PAD + NET_IP_ALIGN;
 
@@ -498,7 +504,11 @@ struct sk_buff *__napi_alloc_skb(struct napi_struct *napi, unsigned int len,
 	if (sk_memalloc_socks())
 		gfp_mask |= __GFP_MEMALLOC;
 
+	nc = &get_locked_var(napi_alloc_cache_lock, napi_alloc_cache);
 	data = __alloc_page_frag(nc, len, gfp_mask);
+	pfmemalloc = nc->pfmemalloc;
+	put_locked_var(napi_alloc_cache_lock, napi_alloc_cache);
+
 	if (unlikely(!data))
 		return NULL;
 
@@ -509,7 +519,7 @@ struct sk_buff *__napi_alloc_skb(struct napi_struct *napi, unsigned int len,
 	}
 
 	/* use OR instead of assignment to avoid clearing of bits in mask */
-	if (nc->pfmemalloc)
+	if (pfmemalloc)
 		skb->pfmemalloc = 1;
 	skb->head_frag = 1;
 
-- 
2.10.2

