From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id 6AB7D6B003D for ; Thu, 19 Mar 2009 12:37:02 -0400 (EDT) From: Nick Piggin Subject: Re: ftruncate-mmap: pages are lost after writing to mmaped file. Date: Fri, 20 Mar 2009 03:36:52 +1100 References: <604427e00903181244w360c5519k9179d5c3e5cd6ab3@mail.gmail.com> <200903200248.22623.nickpiggin@yahoo.com.au> <1237479361.24626.23.camel@twins> In-Reply-To: <1237479361.24626.23.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200903200336.53545.nickpiggin@yahoo.com.au> Sender: owner-linux-mm@kvack.org To: Peter Zijlstra Cc: Ying Han , Jan Kara , Linus Torvalds , Andrew Morton , linux-kernel , linux-mm , guichaz@gmail.com, Alex Khesin , Mike Waychison , Rohit Seth List-ID: On Friday 20 March 2009 03:16:01 Peter Zijlstra wrote: > On Fri, 2009-03-20 at 02:48 +1100, Nick Piggin wrote: > > On Thursday 19 March 2009 10:54:33 Ying Han wrote: > > > On Wed, Mar 18, 2009 at 4:36 PM, Linus Torvalds > > > > > > wrote: > > > > On Wed, 18 Mar 2009, Ying Han wrote: > > > >> > Can you say what filesystem, and what mount-flags you use? Iirc, > > > >> > last time we had MAP_SHARED lost writes it was at least partly > > > >> > triggered by the filesystem doing its own flushing independently > > > >> > of the VM (ie ext3 with "data=journal", I think), so that kind of > > > >> > thing does tend to matter. > > > >> > > > >> /etc/fstab > > > >> "/dev/hda1 / ext2 defaults 1 0" > > > > > > > > Sadly, /etc/fstab is not necessarily accurate for the root > > > > filesystem. At least Fedora will ignore the flags in it. > > > > > > > > What does /proc/mounts say? That should be a more reliable indication > > > > of what the kernel actually does. > > > > > > "/dev/root / ext2 rw,errors=continue 0 0" > > > > No luck with finding the problem yet. > > > > But I think we do have a race in __set_page_dirty_buffers(): > > > > The page may not have buffers between the mapping->private_lock > > critical section and the __set_page_dirty call there. So between > > them, another thread might do a create_empty_buffers which can > > see !PageDirty and thus it will create clean buffers. The page > > will get dirtied by the original thread, but if the buffers are > > clean it can be cleaned without writing out buffers. > > > > Holding mapping->private_lock over the __set_page_dirty should > > fix it, although I guess you'd want to release it before calling > > __mark_inode_dirty so as not to put inode_lock under there. I > > have a patch for this if it sounds reasonable. > > When I first did those dirty tracking patches someone (I think Andrew) > commented no the fact that I did set_page_dirty() under one of these > inner locks.. > > /me frobs around in archives for a bit.. > > - fs/buffers.c try_to_free_buffers(): remove clear_page_dirty() from under > ->private_lock. This seems to be save, since ->private_lock is used to > serialize access to the buffers, not the page itself. > > Hmm, that's a slightly different issue... > > But yeah, your scenario makes heaps of sense. > > Can't we do the TestSetPageDirty() before private_lock ? It's currently > done before tree_lock as well. I think there might be issues with having a clean page but dirty buffers if you do it that way... At any rate, if we can solve the race without swapping the order, I think that would be safer. -- 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