mm/mglru: make memcg_lru->lock irq safe

lru_gen_rotate_memcg() can happen in softirq if memory.soft_limit_in_bytes
is set.  This requires memcg_lru->lock to be irq safe.  Lockdep warns on
this.

This problem only affects memcg v1.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: e4dde56 ("mm: multi-gen LRU: per-node lru_gen_folio lists")
Signed-off-by: Yu Zhao <[email protected]>
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=87c490fd2be656269b6a
Reviewed-by: Yosry Ahmed <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

mm/vmscan.c

@@ -4728,10 +4728,11 @@ static void lru_gen_rotate_memcg(struct lruvec *lruvec, int op)
 {
 	int seg;
 	int old, new;
+	unsigned long flags;
 	int bin = get_random_u32_below(MEMCG_NR_BINS);
 	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
 
-	spin_lock(&pgdat->memcg_lru.lock);
+	spin_lock_irqsave(&pgdat->memcg_lru.lock, flags);
 
 	VM_WARN_ON_ONCE(hlist_nulls_unhashed(&lruvec->lrugen.list));
 
@@ -4766,7 +4767,7 @@ static void lru_gen_rotate_memcg(struct lruvec *lruvec, int op)
 	if (!pgdat->memcg_lru.nr_memcgs[old] && old == get_memcg_gen(pgdat->memcg_lru.seq))
 		WRITE_ONCE(pgdat->memcg_lru.seq, pgdat->memcg_lru.seq + 1);
 
-	spin_unlock(&pgdat->memcg_lru.lock);
+	spin_unlock_irqrestore(&pgdat->memcg_lru.lock, flags);
 }
 
 void lru_gen_online_memcg(struct mem_cgroup *memcg)
@@ -4779,7 +4780,7 @@ void lru_gen_online_memcg(struct mem_cgroup *memcg)
 		struct pglist_data *pgdat = NODE_DATA(nid);
 		struct lruvec *lruvec = get_lruvec(memcg, nid);
 
-		spin_lock(&pgdat->memcg_lru.lock);
+		spin_lock_irq(&pgdat->memcg_lru.lock);
 
 		VM_WARN_ON_ONCE(!hlist_nulls_unhashed(&lruvec->lrugen.list));
 
@@ -4790,7 +4791,7 @@ void lru_gen_online_memcg(struct mem_cgroup *memcg)
 
 		lruvec->lrugen.gen = gen;
 
-		spin_unlock(&pgdat->memcg_lru.lock);
+		spin_unlock_irq(&pgdat->memcg_lru.lock);
 	}
 }
 
@@ -4814,7 +4815,7 @@ void lru_gen_release_memcg(struct mem_cgroup *memcg)
 		struct pglist_data *pgdat = NODE_DATA(nid);
 		struct lruvec *lruvec = get_lruvec(memcg, nid);
 
-		spin_lock(&pgdat->memcg_lru.lock);
+		spin_lock_irq(&pgdat->memcg_lru.lock);
 
 		VM_WARN_ON_ONCE(hlist_nulls_unhashed(&lruvec->lrugen.list));
 
@@ -4826,7 +4827,7 @@ void lru_gen_release_memcg(struct mem_cgroup *memcg)
 		if (!pgdat->memcg_lru.nr_memcgs[gen] && gen == get_memcg_gen(pgdat->memcg_lru.seq))
 			WRITE_ONCE(pgdat->memcg_lru.seq, pgdat->memcg_lru.seq + 1);
 
-		spin_unlock(&pgdat->memcg_lru.lock);
+		spin_unlock_irq(&pgdat->memcg_lru.lock);
 	}
 }