From: Arnd Bergmann <arnd@xxxxxxxx> Subject: 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/20161024155704.3114445-1-arnd@xxxxxxxx Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx> Acked-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx> Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: Christoph Lameter <cl@xxxxxxxxx> Cc: Pekka Enberg <penberg@xxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Laura Abbott <labbott@xxxxxxxxxxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/slub.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff -puN mm/slub.c~slub-avoid-false-postive-warning mm/slub.c --- a/mm/slub.c~slub-avoid-false-postive-warning +++ a/mm/slub.c @@ -3076,7 +3076,7 @@ void kmem_cache_free_bulk(struct kmem_ca 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_); _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
