Re: [patch] mm: bug in set_page_dirty_buffers

[Nick Piggin <npiggin@suse.de>]

On Mon, Oct 09, 2006 at 09:38:06PM -0700, Andrew Morton wrote:
> On Tue, 10 Oct 2006 06:21:44 +0200
> Nick Piggin <npiggin@suse.de> wrote:
> 
> > On Mon, Oct 09, 2006 at 09:14:04PM -0700, Andrew Morton wrote:
> > > Can we convert set_page_dirty_balance() to call set_page_dirty_lock()?
> > 
> > I think so. You can't in zap_pte_range though because you're under
> > spinlocks.
> 
> There we're screwed.
> 
> > Same with try_to_unmap_{one|cluster}, and page_remove_rmap.
> 
> There we can trylock all the pages and bale if any fail.

Hmm, try_to_unmap is OK because the page is already locked. page_remove_rmap
isn't allowed to fail.

> > > And make set_page_dirty_lock() return if the page is already dirty?
> > > 
> > > > I think there are
> > > > a whole lot more problems than just the unmapping path, though. Direct
> > > > IO comes to mind.
> > > 
> > > Why?  direct-io locks the pages while invalidating them, and while marking
> > > them dirty.
> > 
> > Uh, mistaken about dio. Point still stands.
> 
> But where?  locking the page is the preferred way to solve this stuff. 
> (Well, locking the buffers might work, but isn't needed, and locking the
> page covers other stuff)

AFAIKS, it is just fs/buffer.c that is racy. Why can't it use
mapping->private_lock or the buffer bit spinlock?


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