Btrfs: fix regression in btrfs_page_mkwrite() from vm_fault_t conversion

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);

xfstests generic/095 was able to reliably reproduce the errors.

Since out_unlock: is only used for errors, this fix moves it below the
if (!ret2) check we use to return VM_FAULT_LOCKED for success.

Fixes: a528a2415087 (btrfs: change return type of btrfs_page_mkwrite to vm_fault_t)
Signed-off-by: Chris Mason <clm@fb.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index a6bf9e2ff68f..f21f4223d03b 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -9005,13 +9005,14 @@ again:
 
         unlock_extent_cached(io_tree, page_start, page_end, &cached_state);
 
-out_unlock:
         if (!ret2) {
                 btrfs_delalloc_release_extents(BTRFS_I(inode), PAGE_SIZE, true);
                 sb_end_pagefault(inode->i_sb);
                 extent_changeset_free(data_reserved);
                 return VM_FAULT_LOCKED;
         }
+
+out_unlock:
         unlock_page(page);
 out:
         btrfs_delalloc_release_extents(BTRFS_I(inode), PAGE_SIZE, (ret != 0));