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commit f99a8e4373 upstream.
If fast table reloads occur during an ongoing reshape of raid4/5/6
devices the target may race reading a superblock vs the the MD resync
thread; causing an inconclusive reshape state to be read in its
constructor.
lvm2 test lvconvert-raid-reshape-stripes-load-reload.sh can cause
BUG_ON() to trigger in md_run(), e.g.:
"kernel BUG at drivers/md/raid5.c:7567!".
Scenario triggering the bug:
1. the MD sync thread calls end_reshape() from raid5_sync_request()
when done reshaping. However end_reshape() _only_ updates the
reshape position to MaxSector keeping the changed layout
configuration though (i.e. any delta disks, chunk sector or RAID
algorithm changes). That inconclusive configuration is stored in
the superblock.
2. dm-raid constructs a mapping, loading named inconsistent superblock
as of step 1 before step 3 is able to finish resetting the reshape
state completely, and calls md_run() which leads to mentioned bug
in raid5.c.
3. the MD RAID personality's finish_reshape() is called; which resets
the reshape information on chunk sectors, delta disks, etc. This
explains why the bug is rarely seen on multi-core machines, as MD's
finish_reshape() superblock update races with the dm-raid
constructor's superblock load in step 2.
Fix identifies inconclusive superblock content in the dm-raid
constructor and resets it before calling md_run(), factoring out
identifying checks into rs_is_layout_change() to share in existing
rs_reshape_requested() and new rs_reset_inclonclusive_reshape(). Also
enhance a comment and remove an empty line.
Cc: stable@vger.kernel.org
Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
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.