memcg: no irq disable for memcg stock lock

There is no need to disable irqs to use memcg per-cpu stock, so let's just
not do that. One consequence of this change is if the kernel while in
task context has the memcg stock lock and that cpu got interrupted. The
memcg charges on that cpu in the irq context will take the slow path of
memcg charging. However that should be super rare and should be fine in
general.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Shakeel Butt <[e-mail]>
Acked-by: Vlastimil Babka <[e-mail]>
Cc: Alexei Starovoitov <[e-mail]>
Cc: Eric Dumaze <[e-mail]>
Cc: Jakub Kacinski <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Muchun Song <[e-mail]>
Cc: Roman Gushchin <[e-mail]>
Cc: Sebastian Andrzej Siewior <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

mm/memcontrol.c

···
 {
 	struct memcg_stock_pcp *stock;
 	uint8_t stock_pages;
-	unsigned long flags;
 	bool ret = false;
 	int i;
 
 	if (nr_pages > MEMCG_CHARGE_BATCH ||
-	    !local_trylock_irqsave(&memcg_stock.lock, flags))
+	    !local_trylock(&memcg_stock.lock))
 		return ret;
 
 	stock = this_cpu_ptr(&memcg_stock);
···
 		break;
 	}
 
-	local_unlock_irqrestore(&memcg_stock.lock, flags);
+	local_unlock(&memcg_stock.lock);
 
 	return ret;
 }
···
 static void drain_local_memcg_stock(struct work_struct *dummy)
 {
 	struct memcg_stock_pcp *stock;
-	unsigned long flags;
 
 	if (WARN_ONCE(!in_task(), "drain in non-task context"))
 		return;
 
-	local_lock_irqsave(&memcg_stock.lock, flags);
+	local_lock(&memcg_stock.lock);
 
 	stock = this_cpu_ptr(&memcg_stock);
 	drain_stock_fully(stock);
 	clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags);
 
-	local_unlock_irqrestore(&memcg_stock.lock, flags);
+	local_unlock(&memcg_stock.lock);
 }
 
 static void drain_local_obj_stock(struct work_struct *dummy)
···
 	struct memcg_stock_pcp *stock;
 	struct mem_cgroup *cached;
 	uint8_t stock_pages;
-	unsigned long flags;
 	bool success = false;
 	int empty_slot = -1;
 	int i;
···
 	VM_WARN_ON_ONCE(mem_cgroup_is_root(memcg));
 
 	if (nr_pages > MEMCG_CHARGE_BATCH ||
-	    !local_trylock_irqsave(&memcg_stock.lock, flags)) {
+	    !local_trylock(&memcg_stock.lock)) {
 		/*
 		 * In case of larger than batch refill or unlikely failure to
 		 * lock the percpu memcg_stock.lock, uncharge memcg directly.
···
 		WRITE_ONCE(stock->nr_pages[i], nr_pages);
 	}
 
-	local_unlock_irqrestore(&memcg_stock.lock, flags);
+	local_unlock(&memcg_stock.lock);
 }
 
 static bool is_memcg_drain_needed(struct memcg_stock_pcp *stock,