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[ Upstream commit 9973f0fa7d20269fe6fefe6333997fb5914449c1 ] The mdadm test 07layouts randomly produces a kernel hung task deadlock. The deadlock is caused by the suspend_lo/suspend_hi files being set by the mdadm background process during reshape and not being cleared because the process hangs. (Leaving aside the issue of the fragility of freezing kernel tasks by buggy userspace processes...) When the background mdadm process hangs it, is waiting (without a timeout) on a change to the sync_completed file signalling that the reshape has completed. The process is woken up a couple times when the reshape finishes but it is woken up before MD_RECOVERY_RUNNING is cleared so sync_completed_show() reports 0 instead of "none". To fix this, notify the sysfs file in md_reap_sync_thread() after MD_RECOVERY_RUNNING has been cleared. This wakes up mdadm and causes it to continue and write to suspend_lo/suspend_hi to allow IO to continue. Signed-off-by: Logan Gunthorpe <logang@deltatee.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Song Liu <song@kernel.org> Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Sasha Levin <sashal@kernel.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.