lkml.org 
[lkml]   [2019]   [Jun]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH] mm/vmalloc: avoid bogus -Wmaybe-uninitialized warning
On Tue, Jun 18, 2019 at 01:59:20PM -0700, Andrew Morton wrote:
> On Tue, 18 Jun 2019 16:06:22 +0200 Uladzislau Rezki <urezki@gmail.com> wrote:
>
> > On Tue, Jun 18, 2019 at 09:40:28AM -0400, Joel Fernandes wrote:
> > > On Tue, Jun 18, 2019 at 5:27 AM Arnd Bergmann <arnd@arndb.de> wrote:
> > > >
> > > > gcc gets confused in pcpu_get_vm_areas() because there are too many
> > > > branches that affect whether 'lva' was initialized before it gets
> > > > used:
> > > >
> > > > mm/vmalloc.c: In function 'pcpu_get_vm_areas':
> > > > mm/vmalloc.c:991:4: error: 'lva' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> > > > insert_vmap_area_augment(lva, &va->rb_node,
> > > > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > > &free_vmap_area_root, &free_vmap_area_list);
> > > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > > mm/vmalloc.c:916:20: note: 'lva' was declared here
> > > > struct vmap_area *lva;
> > > > ^~~
> > > >
> > > > Add an intialization to NULL, and check whether this has changed
> > > > before the first use.
> > > >
> > > > Fixes: 68ad4a330433 ("mm/vmalloc.c: keep track of free blocks for vmap allocation")
> > > > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> > > > ---
> > > > mm/vmalloc.c | 9 +++++++--
> > > > 1 file changed, 7 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > > > index a9213fc3802d..42a6f795c3ee 100644
> > > > --- a/mm/vmalloc.c
> > > > +++ b/mm/vmalloc.c
> > > > @@ -913,7 +913,12 @@ adjust_va_to_fit_type(struct vmap_area *va,
> > > > unsigned long nva_start_addr, unsigned long size,
> > > > enum fit_type type)
> > > > {
> > > > - struct vmap_area *lva;
> > > > + /*
> > > > + * GCC cannot always keep track of whether this variable
> > > > + * was initialized across many branches, therefore set
> > > > + * it NULL here to avoid a warning.
> > > > + */
> > > > + struct vmap_area *lva = NULL;
> > >
> > > Fair enough, but is this 5-line comment really needed here?
> > >
> > How it is rewritten now, probably not. I would just set it NULL and
> > leave the comment, but that is IMHO. Anyway
> >
>
> I agree - given that the patch does this:
>
> @@ -972,7 +977,7 @@ adjust_va_to_fit_type(struct vmap_area *
> if (type != FL_FIT_TYPE) {
> augment_tree_propagate_from(va);
>
> - if (type == NE_FIT_TYPE)
> + if (lva)
> insert_vmap_area_augment(lva, &va->rb_node,
> &free_vmap_area_root, &free_vmap_area_list);
> }
>
> the comment simply isn't relevant any more. Although I guess this
> might be a bit helpful:
>
> @@ -977,7 +972,7 @@ adjust_va_to_fit_type(struct vmap_area *
> if (type != FL_FIT_TYPE) {
> augment_tree_propagate_from(va);
>
> - if (lva)
> + if (lva) /* type == NE_FIT_TYPE */
> insert_vmap_area_augment(lva, &va->rb_node,
> &free_vmap_area_root, &free_vmap_area_list);
> }
>
That comment makes it much clear, thanks!

--
Vlad Rezki

\
 
 \ /
  Last update: 2019-06-19 12:37    [W:0.045 / U:0.544 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site