Re: [rfc][patch 2/2] buffer, btrfs: fix page_mkwrite error cases

[Chris Mason <chris.mason@oracle.com>]

On Tue, 2009-03-03 at 15:41 +0100, Nick Piggin wrote:
> On Tue, Mar 03, 2009 at 09:26:03AM -0500, Chris Mason wrote:
> > On Tue, 2009-03-03 at 11:41 +0100, Nick Piggin wrote:
> > > page_mkwrite is called with neither the page lock nor the ptl held. This
> > > means a page can be concurrently truncated or invalidated out from underneath
> > > it. Callers are supposed to prevent truncate races themselves, however
> > > previously the only thing they can do in case they hit one is to raise a
> > > SIGBUS. A sigbus is wrong for the case that the page has been invalidated
> > > or truncated within i_size (eg. hole punched). Callers may also have to
> > > perform memory allocations in this path, where again, SIGBUS would be wrong.
> > > 
> > > The previous patch made it possible to properly specify errors. Convert
> > > the generic buffer.c code and btrfs to return sane error values
> > > (in the case of page removed from pagecache, VM_FAULT_NOPAGE will cause the
> > > fault handler to exit without doing anything, and the fault will be retried 
> > > properly).
> > > 
> > 
> > Thanks Nick.  I think the btrfs patch needs an extra } to compile, but
> > it looks fine.
> 
> OK... btrfs is obviously untested :) I just got to btrfs and realised
> that probably most of the non-trivial ones will want fs maintainers to
> take a look. I *think* the following errors should mostly be right:
>
> !page->mapping ==> VM_FAULT_NOPAGE (just cause the VM to retry the fault)
> -ENOMEM ==> VM_FAULT_OOM
> any other error ==> VM_FAULT_SIGBUS
> 

It's no problem, the patch made things more clear than it was before.
You can add an sob for me once it compiles ;)

-chris


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