Commit b4b9e355 authored by Mel Gorman's avatar Mel Gorman Committed by Linus Torvalds
Browse files

netvm: set PF_MEMALLOC as appropriate during SKB processing 



In order to make sure pfmemalloc packets receive all memory needed to
proceed, ensure processing of pfmemalloc SKBs happens under PF_MEMALLOC.
This is limited to a subset of protocols that are expected to be used for
writing to swap.  Taps are not allowed to use PF_MEMALLOC as these are
expected to communicate with userspace processes which could be paged out.

[a.p.zijlstra@chello.nl: Ideas taken from various patches]
[jslaby@suse.cz: Lock imbalance fix]
Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
Acked-by: default avatarDavid S. Miller <davem@davemloft.net>
Cc: Neil Brown <neilb@suse.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Christie <michaelc@cs.wisc.edu>
Cc: Eric B Munson <emunson@mgebm.net>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Christoph Lameter <cl@linux.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0614002b

include/net/sock.h

+5 −0
Original line number Diff line number Diff line
@@ -754,8 +754,13 @@ static inline __must_check int sk_add_backlog(struct sock *sk, struct sk_buff *s 
	return 0;

}



extern int __sk_backlog_rcv(struct sock *sk, struct sk_buff *skb);



static inline int sk_backlog_rcv(struct sock *sk, struct sk_buff *skb)

{

	if (sk_memalloc_socks() && skb_pfmemalloc(skb))

		return __sk_backlog_rcv(sk, skb);



	return sk->sk_backlog_rcv(sk, skb);

}

net/core/dev.c

+47 −6
Original line number Diff line number Diff line
@@ -3155,6 +3155,23 @@ void netdev_rx_handler_unregister(struct net_device *dev) 
}

EXPORT_SYMBOL_GPL(netdev_rx_handler_unregister);



/*

 * Limit the use of PFMEMALLOC reserves to those protocols that implement

 * the special handling of PFMEMALLOC skbs.

 */

static bool skb_pfmemalloc_protocol(struct sk_buff *skb)

{

	switch (skb->protocol) {

	case __constant_htons(ETH_P_ARP):

	case __constant_htons(ETH_P_IP):

	case __constant_htons(ETH_P_IPV6):

	case __constant_htons(ETH_P_8021Q):

		return true;

	default:

		return false;

	}

}



static int __netif_receive_skb(struct sk_buff *skb)

{

	struct packet_type *ptype, *pt_prev;
@@ -3164,14 +3181,27 @@ static int __netif_receive_skb(struct sk_buff *skb) 
	bool deliver_exact = false;

	int ret = NET_RX_DROP;

	__be16 type;

	unsigned long pflags = current->flags;



	net_timestamp_check(!netdev_tstamp_prequeue, skb);



	trace_netif_receive_skb(skb);



	/*

	 * PFMEMALLOC skbs are special, they should

	 * - be delivered to SOCK_MEMALLOC sockets only

	 * - stay away from userspace

	 * - have bounded memory usage

	 *

	 * Use PF_MEMALLOC as this saves us from propagating the allocation

	 * context down to all allocation sites.

	 */

	if (sk_memalloc_socks() && skb_pfmemalloc(skb))

		current->flags |= PF_MEMALLOC;



	/* if we've gotten here through NAPI, check netpoll */

	if (netpoll_receive_skb(skb))

		return NET_RX_DROP;

		goto out;



	orig_dev = skb->dev;
@@ -3191,7 +3221,7 @@ another_round: 
	if (skb->protocol == cpu_to_be16(ETH_P_8021Q)) {

		skb = vlan_untag(skb);

		if (unlikely(!skb))

			goto out;

			goto unlock;

	}



#ifdef CONFIG_NET_CLS_ACT
@@ -3201,6 +3231,9 @@ another_round: 
	}

#endif



	if (sk_memalloc_socks() && skb_pfmemalloc(skb))

		goto skip_taps;



	list_for_each_entry_rcu(ptype, &ptype_all, list) {

		if (!ptype->dev || ptype->dev == skb->dev) {

			if (pt_prev)
@@ -3209,13 +3242,18 @@ another_round: 
		}

	}



skip_taps:

#ifdef CONFIG_NET_CLS_ACT

	skb = handle_ing(skb, &pt_prev, &ret, orig_dev);

	if (!skb)

		goto out;

		goto unlock;

ncls:

#endif



	if (sk_memalloc_socks() && skb_pfmemalloc(skb)

				&& !skb_pfmemalloc_protocol(skb))

		goto drop;



	rx_handler = rcu_dereference(skb->dev->rx_handler);

	if (vlan_tx_tag_present(skb)) {

		if (pt_prev) {
@@ -3225,7 +3263,7 @@ ncls: 
		if (vlan_do_receive(&skb, !rx_handler))

			goto another_round;

		else if (unlikely(!skb))

			goto out;

			goto unlock;

	}



	if (rx_handler) {
@@ -3235,7 +3273,7 @@ ncls: 
		}

		switch (rx_handler(&skb)) {

		case RX_HANDLER_CONSUMED:

			goto out;

			goto unlock;

		case RX_HANDLER_ANOTHER:

			goto another_round;

		case RX_HANDLER_EXACT:
@@ -3268,6 +3306,7 @@ ncls: 
		else

			ret = pt_prev->func(skb, skb->dev, pt_prev, orig_dev);

	} else {

drop:

		atomic_long_inc(&skb->dev->rx_dropped);

		kfree_skb(skb);

		/* Jamal, now you will not able to escape explaining
@@ -3276,8 +3315,10 @@ ncls: 
		ret = NET_RX_DROP;

	}



out:

unlock:

	rcu_read_unlock();

out:

	tsk_restore_flags(current, pflags, PF_MEMALLOC);

	return ret;

}

net/core/sock.c

+16 −0
Original line number Diff line number Diff line
@@ -298,6 +298,22 @@ void sk_clear_memalloc(struct sock *sk) 
}

EXPORT_SYMBOL_GPL(sk_clear_memalloc);



int __sk_backlog_rcv(struct sock *sk, struct sk_buff *skb)

{

	int ret;

	unsigned long pflags = current->flags;



	/* these should have been dropped before queueing */

	BUG_ON(!sock_flag(sk, SOCK_MEMALLOC));



	current->flags |= PF_MEMALLOC;

	ret = sk->sk_backlog_rcv(sk, skb);

	tsk_restore_flags(current, pflags, PF_MEMALLOC);



	return ret;

}

EXPORT_SYMBOL(__sk_backlog_rcv);



#if defined(CONFIG_CGROUPS)

#if !defined(CONFIG_NET_CLS_CGROUP)

int net_cls_subsys_id = -1;

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