[RFC v2 31/34] mm, slub: optionally save/restore irqs in slab_[un]lock()/

[Vlastimil Babka <vbabka@xxxxxxx>]

For PREEMPT_RT we will need to disable irqs for this bit spinlock. As a
preparation, add a flags parameter, and an internal version that takes
additional bool parameter to control irq saving/restoring (the flags
parameter is compile-time unused if the bool is a constant false).

Convert ___cmpxchg_double_slab(), which also comes with the same bool
parameter, to use the internal version.

Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
 mm/slub.c | 49 +++++++++++++++++++++++++++++++------------------
 1 file changed, 31 insertions(+), 18 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index cfd5a7660375..6721169f816d 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -353,18 +353,35 @@ static inline unsigned int oo_objects(struct kmem_cache_order_objects x)
 /*
  * Per slab locking using the pagelock
  */
-static __always_inline void slab_lock(struct page *page)
+static __always_inline void
+__slab_lock(struct page *page, unsigned long *flags, bool disable_irqs)
 {
 	VM_BUG_ON_PAGE(PageTail(page), page);
+	if (disable_irqs)
+		local_irq_save(*flags);
 	bit_spin_lock(PG_locked, &page->flags);
 }
 
-static __always_inline void slab_unlock(struct page *page)
+static __always_inline void
+__slab_unlock(struct page *page, unsigned long *flags, bool disable_irqs)
 {
 	VM_BUG_ON_PAGE(PageTail(page), page);
+	if (disable_irqs)
+		local_irq_restore(*flags);
 	__bit_spin_unlock(PG_locked, &page->flags);
 }
 
+static __always_inline void
+slab_lock(struct page *page, unsigned long *flags)
+{
+	__slab_lock(page, flags, false);
+}
+
+static __always_inline void slab_unlock(struct page *page, unsigned long *flags)
+{
+	__slab_unlock(page, flags, false);
+}
+
 static inline bool ___cmpxchg_double_slab(struct kmem_cache *s, struct page *page,
 		void *freelist_old, unsigned long counters_old,
 		void *freelist_new, unsigned long counters_new,
@@ -384,21 +401,15 @@ static inline bool ___cmpxchg_double_slab(struct kmem_cache *s, struct page *pag
 	{
 		unsigned long flags;
 
-		if (disable_irqs)
-			local_irq_save(flags);
-		slab_lock(page);
+		__slab_lock(page, &flags, disable_irqs);
 		if (page->freelist == freelist_old &&
 					page->counters == counters_old) {
 			page->freelist = freelist_new;
 			page->counters = counters_new;
-			slab_unlock(page);
-			if (disable_irqs)
-				local_irq_restore(flags);
+			__slab_unlock(page, &flags, disable_irqs);
 			return true;
 		}
-		slab_unlock(page);
-		if (disable_irqs)
-			local_irq_restore(flags);
+		__slab_unlock(page, &flags, disable_irqs);
 	}
 
 	cpu_relax();
@@ -1214,11 +1225,11 @@ static noinline int free_debug_processing(
 	struct kmem_cache_node *n = get_node(s, page_to_nid(page));
 	void *object = head;
 	int cnt = 0;
-	unsigned long flags;
+	unsigned long flags, flags2;
 	int ret = 0;
 
 	spin_lock_irqsave(&n->list_lock, flags);
-	slab_lock(page);
+	slab_lock(page, &flags2);
 
 	if (s->flags & SLAB_CONSISTENCY_CHECKS) {
 		if (!check_slab(s, page))
@@ -1251,7 +1262,7 @@ static noinline int free_debug_processing(
 		slab_err(s, page, "Bulk freelist count(%d) invalid(%d)\n",
 			 bulk_cnt, cnt);
 
-	slab_unlock(page);
+	slab_unlock(page, &flags2);
 	spin_unlock_irqrestore(&n->list_lock, flags);
 	if (!ret)
 		slab_fix(s, "Object at 0x%p not freed", object);
@@ -4007,9 +4018,10 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page,
 	void *addr = page_address(page);
 	unsigned long *map;
 	void *p;
+	unsigned long flags;
 
 	slab_err(s, page, text, s->name);
-	slab_lock(page);
+	slab_lock(page, &flags);
 
 	map = get_map(s, page);
 	for_each_object(p, s, addr, page->objects) {
@@ -4020,7 +4032,7 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page,
 		}
 	}
 	put_map(map);
-	slab_unlock(page);
+	slab_unlock(page, &flags);
 #endif
 }
 
@@ -4736,8 +4748,9 @@ static void validate_slab(struct kmem_cache *s, struct page *page,
 {
 	void *p;
 	void *addr = page_address(page);
+	unsigned long flags;
 
-	slab_lock(page);
+	slab_lock(page, &flags);
 
 	if (!check_slab(s, page) || !on_freelist(s, page, NULL))
 		goto unlock;
@@ -4752,7 +4765,7 @@ static void validate_slab(struct kmem_cache *s, struct page *page,
 			break;
 	}
 unlock:
-	slab_unlock(page);
+	slab_unlock(page, &flags);
 }
 
 static int validate_slab_node(struct kmem_cache *s,
-- 
2.31.1