Re: [patch] mm: bug in set_page_dirty_buffers

[Nick Piggin <npiggin@suse.de>]

On Tue, Oct 10, 2006 at 08:48:56AM +0200, Peter Zijlstra wrote:
> On Tue, 2006-10-10 at 07:22 +0200, Nick Piggin wrote:
> > 
> > I disagree because it will lead to horrible hacks because many callers
> > can't sleep. If anything I would much prefer an innermost-spinlock in
> > page->flags that specifically excludes truncate. Actually tree_lock can
> > do that now, provided we pin mapping in all callers to set_page_dirty
> > (which we should do).
> 
> Yeah, but we're hard working to eradicate tree lock; I have ran into

Well yeah, but until then the tree_lock works.

> this problem before; that is, zap_pte_range and co. not being able to
> lock the page. I'd really like to see that fixed.

What's your problem with zap_pte_range?

> In my current concurrent pagecache patches I've abused your PG_nonewrefs
> and made it this page internal (bit)spinlock, but it just doesn't look
> nice to have both this lock and PG_locked.

Regardless of whether or not they spin, PG_locked is an outermost, and
set_page_dirty is called innermost. I don't see why we'd particularly
want to mush them together now, just because we're worried a filesystem
writer wrote buggy code.

It is all well and good to tell me I'm wrong unless I audit all
filesystems, but the fact is that I'm not a filesystem expert, and if
this is what it has come to then either the process has failed, or
we have a large number of filesystems to cull from the tree as
unmaintained.

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