[PATCH] Btrfs: fix regression in btrfs_page_mkwrite() from vm_fault_t conversion

[Chris Mason <clm@fb.com>]

The vm_fault_t conversion commit introduced a ret2 variable for
tracking the integer return values from internal btrfs functions.  It
was sometimes returning VM_FAULT_LOCKED for pages that were actually
invalid and had been removed from the radix.  Something like this:

	ret2 = btrfs_delalloc_reserve_space() // returns zero on success

	lock_page(page)
	if (page->mapping != inode->i_mapping)
	    goto out_unlock;

...

out_unlock:
	if (!ret2) {
		...
		return VM_FAULT_LOCKED;
	}

This ends up triggering this WARNING in btrfs_destroy_inode()
	WARN_ON(BTRFS_I(inode)->block_rsv.size);

The fix used here is to use ret instead of ret2 in our check for success.

Fixes: a528a2415087 (btrfs: change return type of btrfs_page_mkwrite to vm_fault_t)
Signed-off-by: Chris Mason <clm@fb.com>
---
 fs/btrfs/inode.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 193f933..38403aa 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -9013,6 +9013,7 @@ vm_fault_t btrfs_page_mkwrite(struct vm_fault *vmf)
 		goto out_unlock;
 	}
 	ret2 = 0;
+	ret = 0;
 
 	/* page is wholly or partially inside EOF */
 	if (page_start + PAGE_SIZE > size)
@@ -9037,7 +9038,7 @@ vm_fault_t btrfs_page_mkwrite(struct vm_fault *vmf)
 	unlock_extent_cached(io_tree, page_start, page_end, &cached_state);
 
 out_unlock:
-	if (!ret2) {
+	if (!ret) {
 		btrfs_delalloc_release_extents(BTRFS_I(inode), PAGE_SIZE, true);
 		sb_end_pagefault(inode->i_sb);
 		extent_changeset_free(data_reserved);
-- 
2.9.5