netdev - Re: ppoll() stuck on POLLIN while TCP peer is sending

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Date:	Tue, 08 Jan 2013 18:54:42 -0800
From:	Eric Dumazet <erdnetdev@...il.com>
To:	Eric Wong <normalperson@...t.net>, Mel Gorman <mgorman@...e.de>
Cc:	linux-mm@...ck.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: ppoll() stuck on POLLIN while TCP peer is sending

On Tue, 2013-01-08 at 18:32 -0800, Eric Dumazet wrote:

> 
> Hmm, it seems sk_filter() can return -ENOMEM because skb has the
> pfmemalloc() set.

> 
> One TCP socket keeps retransmitting an SKB via loopback, and TCP stack 
> drops the packet again and again.

sock_init_data() sets sk->sk_allocation to GFP_KERNEL

Shouldnt it use (GFP_KERNEL | __GFP_NOMEMALLOC) instead ?



diff --git a/net/core/sock.c b/net/core/sock.c
index bc131d4..76c4b39 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -286,6 +286,7 @@ void sk_set_memalloc(struct sock *sk)
 {
 	sock_set_flag(sk, SOCK_MEMALLOC);
 	sk->sk_allocation |= __GFP_MEMALLOC;
+	sk->sk_allocation &= ~__GFP_NOMEMALLOC;
 	static_key_slow_inc(&memalloc_socks);
 }
 EXPORT_SYMBOL_GPL(sk_set_memalloc);
@@ -294,6 +295,7 @@ void sk_clear_memalloc(struct sock *sk)
 {
 	sock_reset_flag(sk, SOCK_MEMALLOC);
 	sk->sk_allocation &= ~__GFP_MEMALLOC;
+	sk->sk_allocation |= __GFP_NOMEMALLOC;
 	static_key_slow_dec(&memalloc_socks);
 
 	/*
@@ -2230,7 +2232,7 @@ void sock_init_data(struct socket *sock, struct sock *sk)
 
 	init_timer(&sk->sk_timer);
 
-	sk->sk_allocation	=	GFP_KERNEL;
+	sk->sk_allocation	=	GFP_KERNEL | __GFP_NOMEMALLOC;
 	sk->sk_rcvbuf		=	sysctl_rmem_default;
 	sk->sk_sndbuf		=	sysctl_wmem_default;
 	sk->sk_state		=	TCP_CLOSE;


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