aa9509209c
When committing state, the function writecache_flush does the following:
1. write metadata (writecache_commit_flushed)
2. flush disk cache (writecache_commit_flushed)
3. wait for data writes to complete (writecache_wait_for_ios)
4. increase superblock seq_count
5. write the superblock
6. flush disk cache
It may happen that at step 3, when we wait for some write to finish, the
disk may report the write as finished, but the write only hit the disk
cache and it is not yet stored in persistent storage. At step 5 we write
the superblock - it may happen that the superblock is written before the
write that we waited for in step 3. If the machine crashes, it may result
in incorrect data being returned after reboot.
In order to fix the bug, we must swap steps 2 and 3 in the above sequence,
so that we first wait for writes to complete and then flush the disk
cache.
Fixes: 48debafe4f2f ("dm: add writecache target")
Cc: stable@vger.kernel.org # 4.18+
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
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.