linux-kernel - [PATCH] [53/139] af_unix: limit unix_tot

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Message-Id: <20110202004409.4E70E3E09BD@tassilo.jf.intel.com>
Date:	Tue,  1 Feb 2011 16:44:09 -0800 (PST)
From:	Andi Kleen <andi@...stfloor.org>
To:	eric.dumazet@...il.com, davem@...emloft.net, gregkh@...e.de,
	ak@...ux.intel.com, linux-kernel@...r.kernel.org, stable@...nel.org
Subject: [PATCH] [53/139] af_unix: limit unix_tot_inflight

2.6.35-longterm review patch.  If anyone has any objections, please let me know.

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

From: Eric Dumazet <eric.dumazet@...il.com>

[ Upstream commit 9915672d41273f5b77f1b3c29b391ffb7732b84b ]

Vegard Nossum found a unix socket OOM was possible, posting an exploit
program.

My analysis is we can eat all LOWMEM memory before unix_gc() being
called from unix_release_sock(). Moreover, the thread blocked in
unix_gc() can consume huge amount of time to perform cleanup because of
huge working set.

One way to handle this is to have a sensible limit on unix_tot_inflight,
tested from wait_for_unix_gc() and to force a call to unix_gc() if this
limit is hit.

This solves the OOM and also reduce overall latencies, and should not
slowdown normal workloads.

Reported-by: Vegard Nossum <vegard.nossum@...il.com>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
Signed-off-by: Andi Kleen <ak@...ux.intel.com>

---
 net/unix/garbage.c |    7 +++++++
 1 file changed, 7 insertions(+)

Index: linux-2.6.35.y/net/unix/garbage.c
===================================================================
--- linux-2.6.35.y.orig/net/unix/garbage.c
+++ linux-2.6.35.y/net/unix/garbage.c
@@ -259,9 +259,16 @@ static void inc_inflight_move_tail(struc
 }

 static bool gc_in_progress = false;
+#define UNIX_INFLIGHT_TRIGGER_GC 16000

 void wait_for_unix_gc(void)
 {
+	/*
+	 * If number of inflight sockets is insane,
+	 * force a garbage collect right now.
+	 */
+	if (unix_tot_inflight > UNIX_INFLIGHT_TRIGGER_GC && !gc_in_progress)
+		unix_gc();
 	wait_event(unix_gc_wait, gc_in_progress == false);
 }

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