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Subject: Re: nfs mmap adventure (was: 2.6.23-mm1)
From: Peter Zijlstra <peterz@infradead.org>
To: Trond Myklebust <trond.myklebust@fys.uio.no>
Cc: David Howells <dhowells@redhat.com>,
       Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
       Nick Piggin <nickpiggin@yahoo.com.au>
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Date: Mon, 15 Oct 2007 18:38:34 +0200
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On Mon, 2007-10-15 at 11:51 -0400, Trond Myklebust wrote:
> On Mon, 2007-10-15 at 15:06 +0100, David Howells wrote:
> > Peter Zijlstra <peterz@infradead.org> wrote:
> > 
> > > I get funny SIGBUS' like so:
> > > 
> > > fault
> > >   if (->page_mkwrite() < 0)
> > >     nfs_vm_page_mkwrite()
> > >       nfs_write_begin()
> > >         nfs_flush_incompatible()
> > >           nfs_wb_page()
> > >             nfs_wb_page_priority()
> > >               nfs_sync_mapping_wait()
> > >                 nfs_wait_on_request_locked()
> > >                   nfs_wait_on_request()
> > >                     nfs_wait_bit_interruptible()
> > >                       return -ERESTARTSYS
> > >     SIGBUS
> > > 
> > > trying to figure out what to do about this...
> > > 
> > 
> > Hmmm...  It sounds like the fault handler should deliver the appropriate
> > signal, should ->page_mkwrite() return ERESTARTSYS, and then retry the access
> > instruction that caused the fault when the signal handler has finished
> > running.
> 
> If you signal the process before msync() has completed, or before you
> have completed unmapping the region then your writes can potentially be
> lost. Why should we be providing any guarantees beyond that?

Good point, I'm trying to figure out where my signal is comming from.