On Fri, 21 Jan 2011, Hugh Dickins wrote:
> On Thu, 20 Jan 2011, Miklos Szeredi wrote:
> > On Thu, 20 Jan 2011, Christoph Hellwig wrote:
> > > On Thu, Jan 20, 2011 at 01:30:58PM +0100, Miklos Szeredi wrote:
> > > >
> > > > Truncate and hole punching already serialize with i_mutex. Other
> > > > callers of unmap_mapping_range() do not, and it's difficult to get
> > > > i_mutex protection for all callers. In particular ->d_revalidate(),
> > > > which calls invalidate_inode_pages2_range() in fuse, may be called
> > > > with or without i_mutex.
> > >
> > >
> > > Which I think is mostly a fuse problem. I really hate bloating the
> > > generic inode (into which the address_space is embedded) with another
> > > mutex for deficits in rather special case filesystems.
> >
> > As Hugh pointed out unmap_mapping_range() has grown a varied set of
> > callers, which are difficult to fix up wrt i_mutex. Fuse was just an
> > example.
> >
> > I don't like the bloat either, but this is the best I could come up
> > with for fixing this problem generally. If you have a better idea,
> > please share it.
>
> If we start from the point that this is mostly a fuse problem (I expect
> that a thorough audit will show up a few other filesystems too, but
> let's start from this point): you cite ->d_revalidate as a particular
> problem, but can we fix up its call sites so that it is always called
> either with, or much preferably without, i_mutex held? Though actually
> I couldn't find where ->d_revalidate() is called while holding i_mutex.
lookup_one_len
lookup_hash
__lookup_hash
do_revalidate
d_revalidate
I don't see an easy way to get rid of i_mutex for lookup_one_len() and
lookup_hash().
> Failing that, can fuse down_write i_alloc_sem before calling
> invalidate_inode_pages2(_range), to achieve the same exclusion?
> The setattr truncation path takes i_alloc_sem as well as i_mutex,
> though I'm not certain of its full coverage.
Yeah, fuse could use i_alloc_sem or a private mutex, but that would
leave the other uses of unmap_mapping_range() to sort this out for
themsevels.
Thanks,
Miklos
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