linux-kernel - [ 50/53] tcp: do_tcp_sendpages() must try to push data out on oom conditions

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20120518023301.107217981@decadent.org.uk>
Date:	Fri, 18 May 2012 03:33:44 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Willy Tarreau <w@....eu>,
	Eric Dumazet <edumazet@...gle.com>
Subject: [ 50/53] tcp: do_tcp_sendpages() must try to push data out on oom conditions

3.2.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Willy Tarreau <w@....eu>

commit bad115cfe5b509043b684d3a007ab54b80090aa1 upstream.

Since recent changes on TCP splicing (starting with commits 2f533844
"tcp: allow splice() to build full TSO packets" and 35f9c09f "tcp:
tcp_sendpages() should call tcp_push() once"), I started seeing
massive stalls when forwarding traffic between two sockets using
splice() when pipe buffers were larger than socket buffers.

Latest changes (net: netdev_alloc_skb() use build_skb()) made the
problem even more apparent.

The reason seems to be that if do_tcp_sendpages() fails on out of memory
condition without being able to send at least one byte, tcp_push() is not
called and the buffers cannot be flushed.

After applying the attached patch, I cannot reproduce the stalls at all
and the data rate it perfectly stable and steady under any condition
which previously caused the problem to be permanent.

The issue seems to have been there since before the kernel migrated to
git, which makes me think that the stalls I occasionally experienced
with tux during stress-tests years ago were probably related to the
same issue.

This issue was first encountered on 3.0.31 and 3.2.17, so please backport
to -stable.

Signed-off-by: Willy Tarreau <w@....eu>
Acked-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/ipv4/tcp.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 1272a88..6589e11 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -851,8 +851,7 @@ new_segment:
 wait_for_sndbuf:
 		set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
 wait_for_memory:
-		if (copied)
-			tcp_push(sk, flags & ~MSG_MORE, mss_now, TCP_NAGLE_PUSH);
+		tcp_push(sk, flags & ~MSG_MORE, mss_now, TCP_NAGLE_PUSH);

 		if ((err = sk_stream_wait_memory(sk, &timeo)) != 0)
 			goto do_error;
-- 
1.7.10

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/