Re: nfs mmap adventure (was: 2.6.23-mm1)

Peter Zijlstra
2007-10-15T16:39:08Z

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.