Messages in this thread | | | Date | Tue, 8 Feb 2011 10:45:05 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH 1/2] mlock: fix race when munlocking pages in do_wp_page() |
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On Mon, 7 Feb 2011 16:47:35 -0800 Michel Lespinasse <walken@google.com> wrote:
> vmscan can lazily find pages that are mapped within VM_LOCKED vmas, > and set the PageMlocked bit on these pages, transfering them onto the > unevictable list. When do_wp_page() breaks COW within a VM_LOCKED vma, > it may need to clear PageMlocked on the old page and set it on the > new page instead. > > This change fixes an issue where do_wp_page() was clearing PageMlocked on > the old page while the pte was still pointing to it (as well as rmap). > Therefore, we were not protected against vmscan immediately trasnfering > the old page back onto the unevictable list. This could cause pages to > get stranded there forever. > > I propose to move the corresponding code to the end of do_wp_page(), > after the pte (and rmap) have been pointed to the new page. Additionally, > we can use munlock_vma_page() instead of clear_page_mlock(), so that > the old page stays mlocked if there are still other VM_LOCKED vmas > mapping it. > > Signed-off-by: Michel Lespinasse <walken@google.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
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