Subject: [PATCH 21/33] netvm: prevent a TCP specific deadlock

From: Peter Zijlstra <[email-masked]>
Date: Tue, 30 Oct 2007 17:04:22 +0100

It could happen that all !SOCK_MEMALLOC sockets have buffered so much data
that we're over the global rmem limit. This will prevent SOCK_MEMALLOC buffers
from receiving data, which will prevent userspace from running, which is needed
to reduce the buffered data.

Fix this by exempting the SOCK_MEMALLOC sockets from the rmem limit.

Signed-off-by: Peter Zijlstra <[email-masked]>
---
 include/net/sock.h |    7 ++++---
 net/core/stream.c  |    5 +++--
 2 files changed, 7 insertions(+), 5 deletions(-)

Index: linux-2.6/include/net/sock.h
===================================================================
--- linux-2.6.orig/include/net/sock.h
+++ linux-2.6/include/net/sock.h
@@ -743,7 +743,8 @@ static inline struct inode *SOCK_INODE(s
 }
 
 extern void __sk_stream_mem_reclaim(struct sock *sk);
-extern int sk_stream_mem_schedule(struct sock *sk, int size, int kind);
+extern int sk_stream_mem_schedule(struct sock *sk, struct sk_buff *skb,
+		int size, int kind);
 
 #define SK_STREAM_MEM_QUANTUM ((int)PAGE_SIZE)
 
@@ -761,13 +762,13 @@ static inline void sk_stream_mem_reclaim
 static inline int sk_stream_rmem_schedule(struct sock *sk, struct sk_buff *skb)
 {
 	return (int)skb->truesize <= sk->sk_forward_alloc ||
-		sk_stream_mem_schedule(sk, skb->truesize, 1);
+		sk_stream_mem_schedule(sk, skb, skb->truesize, 1);
 }
 
 static inline int sk_stream_wmem_schedule(struct sock *sk, int size)
 {
 	return size <= sk->sk_forward_alloc ||
-	       sk_stream_mem_schedule(sk, size, 0);
+	       sk_stream_mem_schedule(sk, NULL, size, 0);
 }
 
 /* Used by processes to "lock" a socket state, so that
Index: linux-2.6/net/core/stream.c
===================================================================
--- linux-2.6.orig/net/core/stream.c
+++ linux-2.6/net/core/stream.c
@@ -207,7 +207,7 @@ void __sk_stream_mem_reclaim(struct sock
 
 EXPORT_SYMBOL(__sk_stream_mem_reclaim);
 
-int sk_stream_mem_schedule(struct sock *sk, int size, int kind)
+int sk_stream_mem_schedule(struct sock *sk, struct sk_buff *skb, int size, int kind)
 {
 	int amt = sk_stream_pages(size);
 
@@ -224,7 +224,8 @@ int sk_stream_mem_schedule(struct sock *
 	/* Over hard limit. */
 	if (atomic_read(sk->sk_prot->memory_allocated) > sk->sk_prot->sysctl_mem[2]) {
 		sk->sk_prot->enter_memory_pressure();
-		goto suppress_allocation;
+		if (!skb || (skb && !skb_emergency(skb)))
+			goto suppress_allocation;
 	}
 
 	/* Under pressure. */

--