Patch "mm: memcontrol: make per-cpu charge cache IRQ-safe for socket accounting" has been added to the 4.7-stable tree

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

mm: memcontrol: make per-cpu charge cache IRQ-safe for socket accounting

to the 4.7-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:
mm-memcontrol-make-per-cpu-charge-cache-irq-safe-for-socket-accounting.patch
and it can be found in the queue-4.7 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Johannes Weiner <[email protected]>
Date: Mon, 19 Sep 2016 14:44:36 -0700
Subject: mm: memcontrol: make per-cpu charge cache IRQ-safe for socket accounting

From: Johannes Weiner <[email protected]>

commit db2ba40c277dc545bab531671c3f45ac0afea6f8 upstream.

During cgroup2 rollout into production, we started encountering css refcount underflows and css access crashes in the memory controller. Splitting the heavily shared css reference counter into logical users narrowed the imbalance down to the cgroup2 socket memory accounting.

The problem turns out to be the per-cpu charge cache. Cgroup1 had a separate socket counter, but the new cgroup2 socket accounting goes through the common charge path that uses a shared per-cpu cache for all memory that is being tracked. Those caches are safe against scheduling preemption, but not against interrupts - such as the newly added packet receive path. When cache draining is interrupted by network RX taking pages out of the cache, the resuming drain operation will put references of in-use pages, thus causing the imbalance.

Disable IRQs during all per-cpu charge cache operations.

---
 mm/memcontrol.c |   31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

@@ -1797,17 +1797,22 @@ static DEFINE_MUTEX(percpu_charge_mutex)
 static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
 {
 	struct memcg_stock_pcp *stock;
+	unsigned long flags;
 	bool ret = false;
 
 	if (nr_pages > CHARGE_BATCH)
 		return ret;
 
-	stock = &get_cpu_var(memcg_stock);
+	local_irq_save(flags);
+
+	stock = this_cpu_ptr(&memcg_stock);
 	if (memcg == stock->cached && stock->nr_pages >= nr_pages) {
 		stock->nr_pages -= nr_pages;
 		ret = true;
 	}
-	put_cpu_var(memcg_stock);
+
+	local_irq_restore(flags);
+
 	return ret;
 }
 

@@ -1828,15 +1833,18 @@ static void drain_stock(struct memcg_sto
 	stock->cached = NULL;
 }
 
-/*
- * This must be called under preempt disabled or must be called by
- * a thread which is pinned to local cpu.
- */
 static void drain_local_stock(struct work_struct *dummy)
 {
-	struct memcg_stock_pcp *stock = this_cpu_ptr(&memcg_stock);
+	struct memcg_stock_pcp *stock;
+	unsigned long flags;
+
+	local_irq_save(flags);
+
+	stock = this_cpu_ptr(&memcg_stock);
 	drain_stock(stock);
 	clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags);
+
+	local_irq_restore(flags);
 }
 
 /*

@@ -1845,14 +1853,19 @@ static void drain_local_stock(struct wor
  */
 static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
 {
-	struct memcg_stock_pcp *stock = &get_cpu_var(memcg_stock);
+	struct memcg_stock_pcp *stock;
+	unsigned long flags;
+
+	local_irq_save(flags);
 
+	stock = this_cpu_ptr(&memcg_stock);
 	if (stock->cached != memcg) { /* reset if necessary */
 		drain_stock(stock);
 		stock->cached = memcg;
 	}
 	stock->nr_pages += nr_pages;
-	put_cpu_var(memcg_stock);
+
+	local_irq_restore(flags);
 }
 
 /*

Patches currently in stable-queue which might be from [email protected] are

queue-4.7/mm-memcontrol-make-per-cpu-charge-cache-irq-safe-for-socket-accounting.patch queue-4.7/cgroup-duplicate-cgroup-reference-when-cloning-sockets.patch