Patch "tcp: fix possible deadlock in tcp_send_fin()" has been added to the 4.0-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    tcp: fix possible deadlock in tcp_send_fin()

to the 4.0-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     tcp-fix-possible-deadlock-in-tcp_send_fin.patch
and it can be found in the queue-4.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Wed Apr 29 11:59:49 CEST 2015
From: Eric Dumazet <edumazet@google.com>
Date: Tue, 21 Apr 2015 18:32:24 -0700
Subject: tcp: fix possible deadlock in tcp_send_fin()

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit d83769a580f1132ac26439f50068a29b02be535e ]

Using sk_stream_alloc_skb() in tcp_send_fin() is dangerous in
case a huge process is killed by OOM, and tcp_mem[2] is hit.

To be able to free memory we need to make progress, so this
patch allows FIN packets to not care about tcp_mem[2], if
skb allocation succeeded.

In a follow-up patch, we might abort tcp_send_fin() infinite loop
in case TIF_MEMDIE is set on this thread, as memory allocator
did its best getting extra memory already.

This patch reverts d22e15371811 ("tcp: fix tcp fin memory accounting")

Fixes: d22e15371811 ("tcp: fix tcp fin memory accounting")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv4/tcp_output.c |   20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2751,6 +2751,21 @@ begin_fwd:
 	}
 }
 
+/* We allow to exceed memory limits for FIN packets to expedite
+ * connection tear down and (memory) recovery.
+ * Otherwise tcp_send_fin() could loop forever.
+ */
+static void sk_forced_wmem_schedule(struct sock *sk, int size)
+{
+	int amt, status;
+
+	if (size <= sk->sk_forward_alloc)
+		return;
+	amt = sk_mem_pages(size);
+	sk->sk_forward_alloc += amt * SK_MEM_QUANTUM;
+	sk_memory_allocated_add(sk, amt, &status);
+}
+
 /* Send a fin.  The caller locks the socket for us.  This cannot be
  * allowed to fail queueing a FIN frame under any circumstances.
  */
@@ -2773,11 +2788,14 @@ void tcp_send_fin(struct sock *sk)
 	} else {
 		/* Socket is locked, keep trying until memory is available. */
 		for (;;) {
-			skb = sk_stream_alloc_skb(sk, 0, sk->sk_allocation);
+			skb = alloc_skb_fclone(MAX_TCP_HEADER,
+					       sk->sk_allocation);
 			if (skb)
 				break;
 			yield();
 		}
+		skb_reserve(skb, MAX_TCP_HEADER);
+		sk_forced_wmem_schedule(sk, skb->truesize);
 		/* FIN eats a sequence byte, write_seq advanced by tcp_queue_skb(). */
 		tcp_init_nondata_skb(skb, tp->write_seq,
 				     TCPHDR_ACK | TCPHDR_FIN);


Patches currently in stable-queue which might be from edumazet@google.com are

queue-4.0/net-rfs-fix-crash-in-get_rps_cpus.patch
queue-4.0/net-fix-crash-in-build_skb.patch
queue-4.0/tcp-avoid-looping-in-tcp_send_fin.patch
queue-4.0/net-do-not-deplete-pfmemalloc-reserve.patch
queue-4.0/tcp-fix-possible-deadlock-in-tcp_send_fin.patch