Messages in this thread |  | | Subject | Re: [PATCH 3/7] mm,madvise: call soft_offline_page() without MF_COUNT_INCREASED | From | Vlastimil Babka <> | Date | Wed, 25 Nov 2020 19:20:33 +0100 |
| |
On 11/19/20 11:57 AM, Oscar Salvador wrote: > From: Naoya Horiguchi <naoya.horiguchi@nec.com> > > The call to get_user_pages_fast is only to get the pointer to a struct > page of a given address, pinning it is memory-poisoning handler's job, > so drop the refcount grabbed by get_user_pages_fast(). > > Note that the target page is still pinned after this put_page() because > the current process should have refcount from mapping.
Well, but can't it go away due to reclaim, migration or whatever?
> Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com> > Signed-off-by: Oscar Salvador <osalvador@suse.de> > --- > mm/madvise.c | 19 +++++++++++-------- > 1 file changed, 11 insertions(+), 8 deletions(-) > > diff --git a/mm/madvise.c b/mm/madvise.c > index c6b5524add58..7a0f64b93635 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -900,20 +900,23 @@ static int madvise_inject_error(int behavior, > */ > size = page_size(compound_head(page)); > > + /* > + * The get_user_pages_fast() is just to get the pfn of the > + * given address, and the refcount has nothing to do with > + * what we try to test, so it should be released immediately. > + * This is racy but it's intended because the real hardware > + * errors could happen at any moment and memory error handlers > + * must properly handle the race.
Sure they have to. We might just be unexpectedly messing with other process' memory. Or does anything else prevent that?
> + */ > + put_page(page); > + > if (behavior == MADV_SOFT_OFFLINE) { > pr_info("Soft offlining pfn %#lx at process virtual address %#lx\n", > pfn, start); > - ret = soft_offline_page(pfn, MF_COUNT_INCREASED); > + ret = soft_offline_page(pfn, 0); > } else { > pr_info("Injecting memory failure for pfn %#lx at process virtual address %#lx\n", > pfn, start); > - /* > - * Drop the page reference taken by get_user_pages_fast(). In > - * the absence of MF_COUNT_INCREASED the memory_failure() > - * routine is responsible for pinning the page to prevent it > - * from being released back to the page allocator. > - */ > - put_page(page); > ret = memory_failure(pfn, 0); > } > >
|  |