[RFC v2 16/34] mm, slub: validate slab from partial list or page allocator before making it cpu slab

[Vlastimil Babka]

When we obtain a new slab page from node partial list or page allocator, we
assign it to kmem_cache_cpu, perform some checks, and if they fail, we undo
the assignment.

In order to allow doing the checks without irq disabled, restructure the code
so that the checks are done first, and kmem_cache_cpu.page assignment only
after they pass.

Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
---
 mm/slub.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index f4ce372e3dd3..378f1cb040b3 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2729,10 +2729,8 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 	lockdep_assert_irqs_disabled();
 
 	freelist = get_partial(s, gfpflags, node, &page);
-	if (freelist) {
-		c->page = page;
+	if (freelist)
 		goto check_new_page;
-	}
 
 	local_irq_restore(flags);
 	put_cpu_ptr(s->cpu_slab);
@@ -2745,9 +2743,6 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 	}
 
 	local_irq_save(flags);
-	if (c->page)
-		flush_slab(s, c);
-
 	/*
 	 * No other reference to the page yet so we can
 	 * muck around with it freely without cmpxchg
@@ -2756,14 +2751,12 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 	page->freelist = NULL;
 
 	stat(s, ALLOC_SLAB);
-	c->page = page;
 
 check_new_page:
 
 	if (kmem_cache_debug(s)) {
 		if (!alloc_debug_processing(s, page, freelist, addr)) {
 			/* Slab failed checks. Next slab needed */
-			c->page = NULL;
 			local_irq_restore(flags);
 			goto new_slab;
 		} else {
@@ -2782,10 +2775,18 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 		 */
 		goto return_single;
 
+	if (unlikely(c->page))
+		flush_slab(s, c);
+	c->page = page;
+
 	goto load_freelist;
 
 return_single:
 
+	if (unlikely(c->page))
+		flush_slab(s, c);
+	c->page = page;
+
 	deactivate_slab(s, page, get_freepointer(s, freelist), c);
 	local_irq_restore(flags);
 	return freelist;
-- 
2.31.1