[4.2.y-ckt stable] Patch "net: tcp_memcontrol: properly detect ancestor socket pressure" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    net: tcp_memcontrol: properly detect ancestor socket pressure

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt3.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From bbbf4448fb4d5d008bb4fde3efccd5f2b01d95f6 Mon Sep 17 00:00:00 2001
From: Johannes Weiner <hannes at cmpxchg.org>
Date: Thu, 14 Jan 2016 15:20:59 -0800
Subject: net: tcp_memcontrol: properly detect ancestor socket pressure

commit 8c2c2358b236530bc2c79b4c2a447cbdbc3d96d7 upstream.

When charging socket memory, the code currently checks only the local
page counter for excess to determine whether the memcg is under socket
pressure.  But even if the local counter is fine, one of the ancestors
could have breached its limit, which should also force this child to
enter socket pressure.  This currently doesn't happen.

Fix this by using page_counter_try_charge() first.  If that fails, it
means that either the local counter or one of the ancestors are in
excess of their limit, and the child should enter socket pressure.

Fixes: 3e32cb2e0a12 ("mm: memcontrol: lockless page counters")
Signed-off-by: Johannes Weiner <hannes at cmpxchg.org>
Acked-by: David S. Miller <davem at davemloft.net>
Reviewed-by: Vladimir Davydov <vdavydov at virtuozzo.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 include/net/sock.h | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index 639138b..591d303 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1209,11 +1209,13 @@ static inline void memcg_memory_allocated_add(struct cg_proto *prot,
 					      unsigned long amt,
 					      int *parent_status)
 {
-	page_counter_charge(&prot->memory_allocated, amt);
+	struct page_counter *counter;
+
+	if (page_counter_try_charge(&prot->memory_allocated, amt, &counter))
+		return;

-	if (page_counter_read(&prot->memory_allocated) >
-	    prot->memory_allocated.limit)
-		*parent_status = OVER_LIMIT;
+	page_counter_charge(&prot->memory_allocated, amt);
+	*parent_status = OVER_LIMIT;
 }

 static inline void memcg_memory_allocated_sub(struct cg_proto *prot,
--
1.9.1