c67bc98d1f
commit 278d9a243635f26c05ad95dcf9c5a593b9e04dc6 upstream.
Currently, rename whiteout has 3 steps:
1. create tmpfile(which associates old dentry to tmpfile inode) for
whiteout, and store tmpfile to disk
2. link whiteout, associate whiteout inode to old dentry agagin and
store old dentry, old inode, new dentry on disk
3. writeback dirty whiteout inode to disk
Suddenly power-cut or error occurring(eg. ENOSPC returned by budget,
memory allocation failure) during above steps may cause kinds of problems:
Problem 1: ENOSPC returned by whiteout space budget (before step 2),
old dentry will disappear after rename syscall, whiteout file
cannot be found either.
ls dir // we get file, whiteout
rename(dir/file, dir/whiteout, REANME_WHITEOUT)
ENOSPC = ubifs_budget_space(&wht_req) // return
ls dir // empty (no file, no whiteout)
Problem 2: Power-cut happens before step 3, whiteout inode with 'nlink=1'
is not stored on disk, whiteout dentry(old dentry) is written
on disk, whiteout file is lost on next mount (We get "dead
directory entry" after executing 'ls -l' on whiteout file).
Now, we use following 3 steps to finish rename whiteout:
1. create an in-mem inode with 'nlink = 1' as whiteout
2. ubifs_jnl_rename (Write on disk to finish associating old dentry to
whiteout inode, associating new dentry with old inode)
3. iput(whiteout)
Rely writing in-mem inode on disk by ubifs_jnl_rename() to finish rename
whiteout, which avoids middle disk state caused by suddenly power-cut
and error occurring.
Fixes: 9e0a1fff8db56ea ("ubifs: Implement RENAME_WHITEOUT")
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.