Re: msync(2) bug(?), returns AOP_WRITEPAGE_ACTIVATE to userland

[Hugh Dickins <hugh@veritas.com>]

On Tue, 13 Nov 2007, Erez Zadok wrote:
> 
> I posted all of these patches just now.  You're CC'ed.  Hopefully Andrew can
> pull from my unionfs.git branch soon.
> 
> You also reported in your previous emails some hangs/oopses while doing make
> -j 20 in unionfs on top of a single tmpfs, using -mm.  After several days,
> I've not been able to reproduce this w/ my latest set of patches.  If you
> can send me your .config and the specs on the h/w you're using (cpus, mem,
> etc.), I'll see if I can find something similar to it on my end and run the
> same tests.

I'm glad to report that this unionfs, not the one in 2.6.24-rc2-mm1
but the one including those 9 patches you posted, now gets through
my testing with tmpfs without a problem.  I do still get occasional
"unionfs: new lower inode mtime (bindex=0, name=<directory>)"
messages, but nothing worse seen yet: a big improvement.

I deceived myself for a while that the danger of shmem_writepage
hitting its BUG_ON(entry->val) was dealt with too; but that's wrong,
I must go back to working out an escape from that one (despite never
seeing it).

I did think you could clean up the doubled set_page_dirtys,
but it's of no consequence.

Hugh

--- 2.6.24-rc2-mm1+9/fs/unionfs/mmap.c	2007-11-17 12:23:30.000000000 +0000
+++ linux/fs/unionfs/mmap.c	2007-11-17 20:22:29.000000000 +0000
@@ -56,6 +56,7 @@ static int unionfs_writepage(struct page
 	copy_highpage(lower_page, page);
 	flush_dcache_page(lower_page);
 	SetPageUptodate(lower_page);
+	set_page_dirty(lower_page);
 
 	/*
 	 * Call lower writepage (expects locked page).  However, if we are
@@ -66,12 +67,11 @@ static int unionfs_writepage(struct page
 	 * success.
 	 */
 	if (wbc->for_reclaim) {
-		set_page_dirty(lower_page);
 		unlock_page(lower_page);
 		goto out_release;
 	}
+
 	BUG_ON(!lower_mapping->a_ops->writepage);
-	set_page_dirty(lower_page);
 	clear_page_dirty_for_io(lower_page); /* emulate VFS behavior */
 	err = lower_mapping->a_ops->writepage(lower_page, wbc);
 	if (err < 0)

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