slub: avoid false-postive warning

The slub allocator gives us some incorrect warnings when
CONFIG_PROFILE_ANNOTATED_BRANCHES is set, as the unlikely() macro
prevents it from seeing that the return code matches what it was before:

  mm/slub.c: In function `kmem_cache_free_bulk':
  mm/slub.c:262:23: error: `df.s' may be used uninitialized in this function [-Werror=maybe-uninitialized]
  mm/slub.c:2943:3: error: `df.cnt' may be used uninitialized in this function [-Werror=maybe-uninitialized]
  mm/slub.c:2933:4470: error: `df.freelist' may be used uninitialized in this function [-Werror=maybe-uninitialized]
  mm/slub.c:2943:3: error: `df.tail' may be used uninitialized in this function [-Werror=maybe-uninitialized]

I have not been able to come up with a perfect way for dealing with
this, the three options I see are:

 - add a bogus initialization, which would increase the runtime overhead
 - replace unlikely() with unlikely_notrace()
 - remove the unlikely() annotation completely

I checked the object code for a typical x86 configuration and the last
two cases produce the same result, so I went for the last one, which is
the simplest.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnd Bergmann <[email protected]>
Acked-by: Jesper Dangaard Brouer <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Laura Abbott <[email protected]>
Cc: Alexander Potapenko <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/slub.c b/mm/slub.c
index 4a861f265cd70df7e26194159b6562d4d60b07d6..067598a008493fabb68d48120a904943fff4e08c 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3076,7 +3076,7 @@ void kmem_cache_free_bulk(struct kmem_cache *s, size_t size, void **p)
                struct detached_freelist df;
 
                size = build_detached_freelist(s, size, p, &df);
-               if (unlikely(!df.page))
+               if (!df.page)
                        continue;
 
                slab_free(df.s, df.page, df.freelist, df.tail, df.cnt,_RET_IP_);