ec544ec956
commit d1260e2a3f85f4c1010510a15f89597001318b1b upstream.
When a DM cache in writeback mode moves data between the slow and fast
device it can often avoid a copy if the triggering bio either:
i) covers the whole block (no point copying if we're about to overwrite it)
ii) the migration is a promotion and the origin block is currently discarded
Prior to this fix there was a race with case (ii). The discard status
was checked with a shared lock held (rather than exclusive). This meant
another bio could run in parallel and write data to the origin, removing
the discard state. After the promotion the parallel write would have
been lost.
With this fix the discard status is re-checked once the exclusive lock
has been aquired. If the block is no longer discarded it falls back to
the slower full copy path.
Fixes: b29d4986d ("dm cache: significant rework to leverage dm-bio-prison-v2")
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.