Messages in this thread | | | Date | Thu, 4 Jun 2009 19:55:33 +0800 | From | Wu Fengguang <> | Subject | Re: [PATCH] [6/16] HWPOISON: Add various poison checks in mm/memory.c |
| |
On Thu, Jun 04, 2009 at 01:19:15PM +0800, Andi Kleen wrote: > On Thu, Jun 04, 2009 at 12:26:03PM +0800, Wu Fengguang wrote: > > On Thu, Jun 04, 2009 at 02:46:38AM +0800, Andi Kleen wrote: > > > > > > Bail out early when hardware poisoned pages are found in page fault handling. > > > > I suspect this patch is also not absolutely necessary: the poisoned > > page will normally have been isolated already. > > It's needed to prevent new pages comming in when there is a parallel > fault while the memory failure handling is in process. > Otherwise the pages could get remapped in that small window.
This patch makes no difference at least for file pages, including tmpfs.
In filemap_fault(), it will first do find_lock_page(), which will lock the page and then double check if the page->mapping is NULL. If so, it drops that page and re-find/re-create one in the radix tree.
That logic automatically avoids the poisoned page that is being processed, because the poisoned page is now being locked, and when find_lock_page() eventually is able to lock it, its page->mapping will be NULL. So the PageHWPoison(vmf.page) test will never be true for filemap_fault.
shmem_fault() calls shmem_getpage() to get the page, which will return EIO on !uptodate page. It then returns VM_FAULT_SIGBUS on its own.
> > > --- linux.orig/mm/memory.c 2009-06-03 19:36:23.000000000 +0200 > > > +++ linux/mm/memory.c 2009-06-03 19:36:23.000000000 +0200 > > > @@ -2797,6 +2797,9 @@ > > > if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE))) > > > return ret; > > > > > > + if (unlikely(PageHWPoison(vmf.page))) > > > + return VM_FAULT_HWPOISON; > > > + > > > > Direct return with locked page could lockup someone later. > > Either drop this patch or fix it with this check? > > Fair point. Fixed.
OK, thanks.
Fengguang
| |