z3fold: remove preempt disabled sections for RT

Replace get_cpu_ptr() with migrate_disable()+this_cpu_ptr() so RT can take
spinlocks that become sleeping locks.

Signed-off-by Mike Galbraith <efault@gmx.de>

Link: https://lkml.kernel.org/r/20201209145151.18994-3-vitaly.wool@konsulko.com
Signed-off-by: Vitaly Wool <vitaly.wool@konsulko.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/z3fold.c

@@ -623,14 +623,16 @@ static inline void add_to_unbuddied(struct z3fold_pool *pool,
 {
 	if (zhdr->first_chunks == 0 || zhdr->last_chunks == 0 ||
 			zhdr->middle_chunks == 0) {
-		struct list_head *unbuddied = get_cpu_ptr(pool->unbuddied);
-
+		struct list_head *unbuddied;
 		int freechunks = num_free_chunks(zhdr);
+
+		migrate_disable();
+		unbuddied = this_cpu_ptr(pool->unbuddied);
 		spin_lock(&pool->lock);
 		list_add(&zhdr->buddy, &unbuddied[freechunks]);
 		spin_unlock(&pool->lock);
 		zhdr->cpu = smp_processor_id();
-		put_cpu_ptr(pool->unbuddied);
+		migrate_enable();
 	}
 }
 
@@ -880,8 +882,9 @@ static inline struct z3fold_header *__z3fold_alloc(struct z3fold_pool *pool,
 	int chunks = size_to_chunks(size), i;
 
 lookup:
+	migrate_disable();
 	/* First, try to find an unbuddied z3fold page. */
-	unbuddied = get_cpu_ptr(pool->unbuddied);
+	unbuddied = this_cpu_ptr(pool->unbuddied);
 	for_each_unbuddied_list(i, chunks) {
 		struct list_head *l = &unbuddied[i];
 
@@ -899,7 +902,7 @@ lookup:
 		    !z3fold_page_trylock(zhdr)) {
 			spin_unlock(&pool->lock);
 			zhdr = NULL;
-			put_cpu_ptr(pool->unbuddied);
+			migrate_enable();
 			if (can_sleep)
 				cond_resched();
 			goto lookup;
@@ -913,7 +916,7 @@ lookup:
 		    test_bit(PAGE_CLAIMED, &page->private)) {
 			z3fold_page_unlock(zhdr);
 			zhdr = NULL;
-			put_cpu_ptr(pool->unbuddied);
+			migrate_enable();
 			if (can_sleep)
 				cond_resched();
 			goto lookup;
@@ -928,7 +931,7 @@ lookup:
 		kref_get(&zhdr->refcount);
 		break;
 	}
-	put_cpu_ptr(pool->unbuddied);
+	migrate_enable();
 
 	if (!zhdr) {
 		int cpu;