From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 7 Mar 2007 12:37:18 +0100 From: Nick Piggin Subject: Re: [patch 8/6] mm: fix cpdfio vs fault race Message-ID: <20070307113717.GB18704@wotan.suse.de> References: <20070307110429.GF5555@wotan.suse.de> <20070307032038.f08333a8.akpm@linux-foundation.org> <20070307033400.83922b12.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070307033400.83922b12.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: miklos@szeredi.hu, Linux Memory Management List , linux-kernel@vger.kernel.org, Linus Torvalds List-ID: On Wed, Mar 07, 2007 at 03:34:00AM -0800, Andrew Morton wrote: > On Wed, 7 Mar 2007 03:20:38 -0800 Andrew Morton wrote: > > > > > > =================================================================== > > > --- linux-2.6.orig/mm/memory.c > > > +++ linux-2.6/mm/memory.c > > > @@ -1676,6 +1676,17 @@ gotten: > > > unlock: > > > pte_unmap_unlock(page_table, ptl); > > > if (dirty_page) { > > > + /* > > > + * Yes, Virginia, this is actually required to prevent a race > > > + * with clear_page_dirty_for_io() from clearing the page dirty > > > + * bit after it clear all dirty ptes, but before a racing > > > + * do_wp_page installs a dirty pte. > > > + * > > > + * do_fault is protected similarly by holding the page lock > > > + * after the dirty pte is installed. > > > + */ > > > + lock_page(dirty_page); > > > + unlock_page(dirty_page); > > > set_page_dirty_balance(dirty_page); > > > put_page(dirty_page); > > > > Yes, I think that'll plug it. A wait_on_page_locked() should suffice. > > Or will it? Suppose after the unlock_page() a _second_ > clear_page_dirty_for_io() gets run - the same thing happens? > > Extending the lock_page() coverage around the set_page_dirty() would > prevent that. > > I guess not needed - the second clear_page_dirty_for_io() will have cleaned the > pte. Yeah, all we need to do is keep page faults out of that little window in clear_page_dirty_for_io() where I stuck the comment. -- 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/ . Don't email: email@kvack.org