Subject: Re: nfs mmap adventure (was: 2.6.23-mm1)
From: Trond Myklebust <trond.myklebust@fys.uio.no>
To: David Howells <dhowells@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
       Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
       Nick Piggin <nickpiggin@yahoo.com.au>
In-Reply-To: <21859.1192457172@redhat.com>
References: <1192451324.27435.71.camel@twins>
	 <20071011213126.cf92efb7.akpm@linux-foundation.org>
	 <21859.1192457172@redhat.com>
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Date: Mon, 15 Oct 2007 11:51:29 -0400
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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?

Trond

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