Messages in this thread | | | Date | Fri, 18 Nov 2011 17:11:28 +0100 | From | Michal Hocko <> | Subject | Re: [PATCH] hugetlb: detect race if fail to COW |
| |
On Fri 18-11-11 23:23:12, Hillf Danton wrote: > On Fri, Nov 18, 2011 at 11:07 PM, Michal Hocko <mhocko@suse.cz> wrote: > > On Fri 18-11-11 22:04:37, Hillf Danton wrote: > >> In the error path that we fail to allocate new huge page, before try again, we > >> have to check race since page_table_lock is re-acquired. > > > > I do not think we can race here because we are serialized by > > hugetlb_instantiation_mutex AFAIU. Without this lock, however, we could > > fall into avoidcopy and shortcut despite the fact that other thread has > > already did the job. > > > > The mutex usage is not obvious in hugetlb_cow so maybe we want to be > > explicit about it (either a comment or do the recheck). > > > > Then the following check is unnecessary, no?
Hmm, thinking about it some more, I guess we have to recheck because we can still race with page migration. So we need you patch.
Reviewed-by: Michal Hocko <mhocko@suse.cz>
> > Thanks, > Hillf > > /* > * Retake the page_table_lock to check for racing updates > * before the page tables are altered > */ > spin_lock(&mm->page_table_lock); > ptep = huge_pte_offset(mm, address & huge_page_mask(h)); > if (likely(pte_same(huge_ptep_get(ptep), pte))) { > /* Break COW */ > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ > Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
-- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic
| |