Messages in this thread |  | | | From | Nick Piggin <> | | Subject | Re: [PATCH 24/28] AFS: Add a function to excise a rejected write from the pagecache [try #2] | | Date | Fri, 21 Dec 2007 12:11:14 +1100 | |
On Friday 21 December 2007 05:49, David Howells wrote:
> Nick Piggin <nickpiggin@yahoo.com.au> wrote:
> > > Nick Piggin <nickpiggin@yahoo.com.au> wrote:
> > > > This reintroduces the fault vs truncate race window, which must be
> > > > fixed.
> > >
> > > Hmmm... perhaps.
> >
> > What do you mean by perhaps?
>
> I mean 'perhaps'. I'm not sure I remember what the race was, so I can't
> evaluate whether or not the same race crops up in AFS too. So: can you
> describe the race please.
It's in the changelogs.
> > No, you could do writeback caching but disallow read of dirty data.
>
> Someone might already have read-access via mmap at the point someone
> attempts to write to an mmapped region. That means that I'd have to revoke
> the read access of the first someone before letting the write take place.
>
> Does NFS do this?
I don't know. But yeah I guess it's tricky. Still, if I was writing a
filesystem, I'd focus on behavioural niceness/correctness above
performance, but maybe that's not realistic.
> > > > But otherwise I guess if you really want to discard the dirty data
> > > > after a failed writeback attempt, what's wrong with just
> > > > invalidate_inode_pages2?
> > >
> > > Erm... Because it deadlocks?
> >
> > Why don't you call it after calling end_page_writeback?
>
> Because then there can be a race over who gets to flush the dead write.
You should solve it in your filesystem.
> Actually, this may no longer be a problem with your write_begin() changes.
> I'll need to have another look at those.
>
> Besides, I don't agree that invalidate_inode_pages2() is necessarily the
> right way to do things.
Why?
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