[PATCH v4 18/35] mm, slub: stop disabling irqs around get_partial()

[Vlastimil Babka <vbabka@xxxxxxx>]

The function get_partial() does not need to have irqs disabled as a whole. It's
sufficient to convert spin_lock operations to their irq saving/restoring
versions.

As a result, it's now possible to reach the page allocator from the slab
allocator without disabling and re-enabling interrupts on the way.

Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
 mm/slub.c | 22 ++++++++--------------
 1 file changed, 8 insertions(+), 14 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index f7c6cebb524d..b4a62aa00ae2 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1993,11 +1993,12 @@ static inline bool pfmemalloc_match(struct page *page, gfp_t gfpflags);
  * Try to allocate a partial slab from a specific node.
  */
 static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n,
-			      struct page **ret_page, gfp_t flags)
+			      struct page **ret_page, gfp_t gfpflags)
 {
 	struct page *page, *page2;
 	void *object = NULL;
 	unsigned int available = 0;
+	unsigned long flags;
 	int objects;
 
 	/*
@@ -2009,11 +2010,11 @@ static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n,
 	if (!n || !n->nr_partial)
 		return NULL;
 
-	spin_lock(&n->list_lock);
+	spin_lock_irqsave(&n->list_lock, flags);
 	list_for_each_entry_safe(page, page2, &n->partial, slab_list) {
 		void *t;
 
-		if (!pfmemalloc_match(page, flags))
+		if (!pfmemalloc_match(page, gfpflags))
 			continue;
 
 		t = acquire_slab(s, n, page, object == NULL, &objects);
@@ -2034,7 +2035,7 @@ static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n,
 			break;
 
 	}
-	spin_unlock(&n->list_lock);
+	spin_unlock_irqrestore(&n->list_lock, flags);
 	return object;
 }
 
@@ -2749,8 +2750,10 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 			local_irq_restore(flags);
 			goto reread_page;
 		}
-		if (unlikely(!slub_percpu_partial(c)))
+		if (unlikely(!slub_percpu_partial(c))) {
+			local_irq_restore(flags);
 			goto new_objects; /* stolen by an IRQ handler */
+		}
 
 		page = c->page = slub_percpu_partial(c);
 		slub_set_percpu_partial(c, page);
@@ -2759,18 +2762,9 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 		goto redo;
 	}
 
-	local_irq_save(flags);
-	if (unlikely(c->page)) {
-		local_irq_restore(flags);
-		goto reread_page;
-	}
-
 new_objects:
 
-	lockdep_assert_irqs_disabled();
-
 	freelist = get_partial(s, gfpflags, node, &page);
-	local_irq_restore(flags);
 	if (freelist)
 		goto check_new_page;
 
-- 
2.32.0