Re: [PATCH 1/2]: Fix BUG in cancel_dirty_pages on XFS

[Nick Piggin <nickpiggin@xxxxxxxxxxxx>]

Peter Zijlstra wrote:
> On Thu, 2007-01-25 at 00:43 +1100, Nick Piggin wrote:
>
>
> > > Have you seen the new launder_page() a_op? called from
> > > invalidate_inode_pages2_range()
> >
> > It would have been nice to make that one into a more potentially
> > useful generic callback.
>
>
> That can still be done when the need arises, right?

Yeah I guess so.

> > But why was it introduced, exactly? I can't tell from the code or
> > the discussion why NFS couldn't start the IO, and signal the caller
> > to wait_on_page_writeback and retry? That seemed to me like the
> > convetional fix.
>
>
> to quote a bit:
>
> On Tue, 19 Dec 2006 18:19:38 -0500
> Trond Myklebust <trond.myklebust@xxxxxxxxxx> wrote:
>
>
> >    NFS: Fix race in nfs_release_page()
> >    
> >    invalidate_inode_pages2() may set the dirty bit on a page owing to the call
> >    to unmap_mapping_range() after the page was locked. In order to fix this,
> >    NFS has hooked the releasepage() method. This, however leads to deadlocks
> >    in other parts of the VM.
>
>
> and:
>
>
> > > Now, arguably the VM shouldn't be calling try_to_release_page() with
> > > __GFP_FS when it's holding a lock on a page.
> > >
> > > But otoh, NFS should never be running lock_page() within nfs_release_page()
> > > against the page which was passed into nfs_release_page().  It'll deadlock
> > > for sure.
> >
> > The reason why it is happening is that the last dirty page from that
> > inode gets cleaned, resulting in a call to dput().

OK but what's the problem with just failing to release the page if it
is dirty, I wonder? In the worst case, page reclaim will just end up
doing a writeout to clean it.

--
SUSE Labs, Novell Inc.
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