tree 25dcd0b7dc78562d01c7865527d3fd46d6f99bb6
parent 1b9b922a3a601b0c99a095ffafed61fcf6ebe0b7
author Chris Mason <clm@fb.com> 1450136444 -0800
committer Chris Mason <clm@fb.com> 1450199378 -0800

Btrfs: check prepare_uptodate_page() error code earlier

prepare_pages() may end up calling prepare_uptodate_page() twice if our
write only spans a single page.  But if the first call returns an error,
our page will be unlocked and its not safe to call it again.

This bug goes all the way back to 2011, and it's not something commonly
hit.

While we're here, add a more explicit check for the page being truncated
away.  The bare lock_page() alone is protected only by good thoughts and
i_mutex, which we're sure to regret eventually.

Reported-by: Dave Jones <dsj@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>