[parisc-linux] rmap: parisc __flush_dcache_page

[Hugh Dickins]

On Thu, 8 Apr 2004, Andrea Arcangeli wrote:
> On Thu, Apr 08, 2004 at 09:40:37AM -0500, James Bottomley wrote:
> > Whatever seems most convenient that won't impact the flushing fast path,
> > I suppose.  It's one of the hottest paths in the system since all data
> > transfers go through it for user visibility.
> 
> you'd need to take a semaphore there to be safe, so it's basically
> unfixable since you can't sleep or just trylock.

It's not fixable via the i_shared_sem, but we can add another layer
of spin_lock around the i_mmap* list/tree manipulations, one that
preprocesses away to nothing on all arches but parisc and arm, and
is used in their __flush_dcache_page.  *Not* the page_table_lock ;)
Unappealing, but a lot better than leaving them unsafe.

Hugh