Re: oops in nfs_flush_incompatible (and possible fix?)

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On Thu, 2010-12-09 at 14:01 -0500, Jeff Layton wrote:
> On Tue, 07 Dec 2010 23:19:32 -0500
> Trond Myklebust <Trond.Myklebust@xxxxxxxxxx> wrote:
> 
> > On Tue, 2010-12-07 at 22:45 -0500, Trond Myklebust wrote:
> > > On Tue, 2010-12-07 at 22:17 -0500, Trond Myklebust wrote:
> > > > OK... I think I see why the hang:
> > > > 
> > > > I believe that it is basically due to nfs_clear_page_tag_locked() making
> > > > the assumption that if req->wb_page != NULL, then the corresponding
> > > > nfsi->nfs_page_tree lock tag needs to be cleared.
> > > > 
> > > > Maybe we can do that differently by just setting a flag to indicate
> > > > whether or not this request is mapped into the radix tree...
> > > 
> > > The following patch is completely untested, but should do the trick....
> > 
> > ...and it appears to work correctly for me.
> > 
> 
> Hi Trond,
> 
> I've gotten some preliminary results with the patch that I backported
> to RHEL5:
> 
> -----------------------[snip]------------------
> 
> FYI, this version has been running now for about 18 hours on
> the same [host] where I originally observed this problem.  A full run takes 48
> hours, but this is well beyond the normal point of failure so I thought
> I'd share preliminary results.
> 
> -----------------------[snip]------------------
> 
> So, it looks good so far. If you like, you can add my. I'll let you
> know once the run is done.
> 
> Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
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Thanks!

BTW: the reason why the PG_MAPPER is not critical in the RHEL-5 back
port is because the BKL keeps you safe w.r.t. races between the tests in
nfs_flush_incompatible() and the nfs_clear_request call in
nfs_inode_remove_request().

Cheers
  Trond

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@xxxxxxxxxx
www.netapp.com

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