Re: [PATCH 12/17] [LogFS] readwrite.c

[Pekka Enberg <penberg@cs.helsinki.fi>]

Hi Joern,

(Dunno who to CC, really, so lets see if I can trick Andrew or Hugh
into looking at the issue.)

On Fri, Nov 20, 2009 at 9:38 PM, Joern Engel <joern@logfs.org> wrote:
> +static void logfs_lock_write_page(struct page *page)
> +{
> +       int loop = 0;
> +
> +       while (unlikely(!trylock_page(page))) {
> +               if (loop++ > 0x1000) {
> +                       /* Has been observed once so far... */
> +                       printk(KERN_ERR "stack at %p\n", &loop);
> +                       BUG();
> +               }
> +               if (PagePreLocked(page)) {
> +                       /* Holder of page lock is waiting for us, it
> +                        * is safe to use this page. */
> +                       break;
> +               }
> +               /* Some other process has this page locked and has
> +                * nothing to do with us.  Wait for it to finish.
> +                */
> +               schedule();
> +       }
> +       BUG_ON(!PageLocked(page));
> +}

What's the purpose of PagePreLocked()? The above function looks pretty
fragile for a filesystem to me.

                        Pekka