lkml.org 
[lkml]   [2018]   [Jun]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] mm: drop VM_BUG_ON from __get_free_pages
On Tue 26-06-18 15:57:39, Vlastimil Babka wrote:
> On 06/22/2018 06:28 PM, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@suse.com>
> >
> > There is no real reason to blow up just because the caller doesn't know
> > that __get_free_pages cannot return highmem pages. Simply fix that up
> > silently. Even if we have some confused users such a fixup will not be
> > harmful.
> >
> > Signed-off-by: Michal Hocko <mhocko@suse.com>
> > ---
> > Hi Andrew,
> > previously posted [1] but it fell through cracks. Can we merge it now?
> >
> > [1] http://lkml.kernel.org/r/20171129160446.jluzpv3n6mjc3fwv@dhcp22.suse.cz
> >
> > mm/page_alloc.c | 10 +++-------
> > 1 file changed, 3 insertions(+), 7 deletions(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 1521100f1e63..5f56f662a52d 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -4402,18 +4402,14 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order, int preferred_nid,
> > EXPORT_SYMBOL(__alloc_pages_nodemask);
> >
> > /*
> > - * Common helper functions.
> > + * Common helper functions. Never use with __GFP_HIGHMEM because the returned
> > + * address cannot represent highmem pages. Use alloc_pages and then kmap if
> > + * you need to access high mem.
> > */
> > unsigned long __get_free_pages(gfp_t gfp_mask, unsigned int order)
> > {
> > struct page *page;
> >
> > - /*
> > - * __get_free_pages() returns a virtual address, which cannot represent
> > - * a highmem page
> > - */
> > - VM_BUG_ON((gfp_mask & __GFP_HIGHMEM) != 0);
> > -
> > page = alloc_pages(gfp_mask, order);
>
> The previous version had also replaced the line above with:
>
> + page = alloc_pages(gfp_mask & ~__GFP_HIGHMEM, order);
>
> This one doesn't, yet you say "fix that up silently". Bug?

got lost somewhere on the way during the discussion. Thanks for spotting
that.

Andrew, could you add gfp_mask & ~__GFP_HIGHMEM please? Or should I
resubmit?

--
Michal Hocko
SUSE Labs

\
 
 \ /
  Last update: 2018-06-26 16:45    [W:0.064 / U:0.608 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site