slab: __GFP_ZERO is incompatible with a constructor

__GFP_ZERO requests that the object be initialised to all-zeroes, while
the purpose of a constructor is to initialise an object to a particular
pattern.  We cannot do both.  Add a warning to catch any users who
mistakenly pass a __GFP_ZERO flag when allocating a slab with a
constructor.

Link: http://lkml.kernel.org/r/20180412191322.GA21205@bombadil.infradead.org
Fixes: d07dbea46405 ("Slab allocators: support __GFP_ZERO in all allocators")
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/slab.c b/mm/slab.c
index 2f30825..c1fe809 100644 (file)
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -2665,6 +2665,7 @@ static struct page *cache_grow_begin(struct kmem_cache *cachep,
                                invalid_mask, &invalid_mask, flags, &flags);
                dump_stack();
        }
+       WARN_ON_ONCE(cachep->ctor && (flags & __GFP_ZERO));
        local_flags = flags & (GFP_CONSTRAINT_MASK|GFP_RECLAIM_MASK);
 
        check_irq_off();
@@ -3071,6 +3072,7 @@ static inline void cache_alloc_debugcheck_before(struct kmem_cache *cachep,
 static void *cache_alloc_debugcheck_after(struct kmem_cache *cachep,
                                gfp_t flags, void *objp, unsigned long caller)
 {
+       WARN_ON_ONCE(cachep->ctor && (flags & __GFP_ZERO));
        if (!objp)
                return objp;
        if (cachep->flags & SLAB_POISON) {

diff --git a/mm/slob.c b/mm/slob.c
index 623e8a5..307c2c9 100644 (file)
--- a/mm/slob.c
+++ b/mm/slob.c
@@ -555,8 +555,10 @@ static void *slob_alloc_node(struct kmem_cache *c, gfp_t flags, int node)
                                            flags, node);
        }
 
-       if (b && c->ctor)
+       if (b && c->ctor) {
+               WARN_ON_ONCE(flags & __GFP_ZERO);
                c->ctor(b);
+       }
 
        kmemleak_alloc_recursive(b, c->size, 1, c->flags, flags);
        return b;

diff --git a/mm/slub.c b/mm/slub.c
index 44aa784..dc96040 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2444,6 +2444,8 @@ static inline void *new_slab_objects(struct kmem_cache *s, gfp_t flags,
        struct kmem_cache_cpu *c = *pc;
        struct page *page;
 
+       WARN_ON_ONCE(s->ctor && (flags & __GFP_ZERO));
+
        freelist = get_partial(s, flags, node, c);
 
        if (freelist)