Christoph Lameter <[email protected]> wrote:
>
> On Tue, 10 Jan 2006, Andrew Morton wrote:
>
> > Christoph Lameter <[email protected]> wrote:
> > >
> > > + spin_lock(&mapping->private_lock);
> > > +
> > > + bh = head;
> > > + do {
> > > + get_bh(bh);
> > > + lock_buffer(bh);
> > > + bh = bh->b_this_page;
> > > +
> > > + } while (bh != head);
> > > +
> >
> > Guys, lock_buffer() sleeps and cannot be called inside spinlock.
>
> I took it the way it was in the hotplug patches.We are taking the
> spinlock here to protect the scan over the list of bh's of this page
> right?
>
> Is it not sufficient to have the page locked to guarantee that the list of
> buffers is not changed? Seems that ext3 does that (see
> ext3_ordered_writepage() etc).
Yes, the page lock protects the buffer ring.
> like this?
>
> Index: linux-2.6.15/fs/buffer.c
> ===================================================================
> --- linux-2.6.15.orig/fs/buffer.c 2006-01-10 22:13:37.000000000 -0800
> +++ linux-2.6.15/fs/buffer.c 2006-01-10 22:37:28.000000000 -0800
> @@ -3070,8 +3070,6 @@ int buffer_migrate_page(struct page *new
> if (migrate_page_remove_references(newpage, page, 3))
> return -EAGAIN;
>
> - spin_lock(&mapping->private_lock);
> -
> bh = head;
> do {
> get_bh(bh);
> @@ -3094,11 +3092,9 @@ int buffer_migrate_page(struct page *new
> } while (bh != head);
>
> SetPagePrivate(newpage);
> - spin_unlock(&mapping->private_lock);
>
> migrate_page_copy(newpage, page);
>
> - spin_lock(&mapping->private_lock);
> bh = head;
> do {
> unlock_buffer(bh);
> @@ -3106,7 +3102,6 @@ int buffer_migrate_page(struct page *new
> bh = bh->b_this_page;
>
> } while (bh != head);
> - spin_unlock(&mapping->private_lock);
>
> return 0;
> }
Seems right, I think.
So let's see. Suppose the kernel is about to dink with a page's buffer
ring. It does:
get_page(page);
lock_page(page);
dink_with(page_buffers(page));
how do these patches ensure that the page doesn't get migrated under my
feet?
-
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