Re: [patch 00/13] vfs: add helpers to check r/o bind mounts

[Al Viro <viro@ZenIV.linux.org.uk>]

On Thu, Apr 24, 2008 at 04:16:52PM +0200, Miklos Szeredi wrote:
> > And I certainly agree that it ought to be replaced by will/wont pair to
> > close the remount race.  One that had been there all along.  All fh_verify()
> > callers of that kind need it - we want to pull mnt_{will,wont}_write()
> > pair into callers *and* stretch to protect the entire relevant area.
> > 
> > Which contains vfs_...() in case of nfsd_create, etc.  See what I mean?
> > That's exactly the thing I'd been talking about - the area we want to
> > cover is _bigger_ than vfs_...() and contains nfsd-specific logic.  IOW,
> > doesn't get folded into any VFS-provided helper.
> 
> I still don't get it why it needs to cover nfsd-specifi logic.  What
> does nfsd have to do with r/o mounts?

Explain to me again, how fh_verify() manages to contain no nfsd-specific
logics.  Please.  You are right - we do have races there.  Always had.
And nfsd_permission() is the next target for continuation of ro-bind
series.  Assuming that we don't simply make r/w export to hold will_write
all along, in which case all these checks around calls of vfs_...() in
there simply go away - that's also an arguable option.