On Mon, 24 Oct 2016 17:56:13 +0200 Arnd Bergmann <a...@arndb.de> wrote:
> 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. If the object code is the same, then I've fine with this solution, as the performance should then also be the same. I do have micro-benchmark module there to verify the performance: https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/mm/slab_bulk_test01.c Acked-by: Jesper Dangaard Brouer <bro...@redhat.com> > Signed-off-by: Arnd Bergmann <a...@arndb.de> > --- > mm/slub.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/slub.c b/mm/slub.c > index 2b3e740609e9..68b84f93d38d 100644 > --- 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_); -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat Author of http://www.iptv-analyzer.org LinkedIn: http://www.linkedin.com/in/brouer
