On Fri, 25 May 2007 00:08:43 +0100
David Howells <[email protected]> wrote:
> Andrew Morton <[email protected]> wrote:
>
> > hm. I don't see why that race window would be a problem in practice: the
> > page-exciser does a lock_page();wait_on_page_writeback() as normal, then
> > proceeds with its business?
>
> No. The page-exciser ends (cancels) PG_writeback, not waits for it (something
> has to clear the flag). The problem is that the truncation routines may be
> sat there holding a lock on the page whilst waiting for PG_writeback to go
> away - so we have to clear PG_writeback before we can think about getting
> PG_lock:-(
But we already covered that? Your exciser can do an unconditional
end_page_writeback(), because it is this thread of control which did the
set_page_writeback(). So we end up with:
end_page_writeback(page);
lock_page(page);
wait_on_page_writeback(page);
<now nail it>
> > But given that this doesn't work right for some reason, can we use PG_error
> > and then handle that appropriately in the filesystem's ->prepare_write() and
> > ->page_mkwrite()?
>
> Possibly, though I'd rather they didn't see such a page.
Well someone needs to be taught all about this case. Question is, should
it be the VFS, or should it just be the address_space(s) which brought
this state about, and which care about it?
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