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When a node fails, user space informs dlm of the node failure, and dlm instructs gfs2 on the surviving nodes to perform journal recovery. It does this by calling various callback functions in lock_dlm.c. To mark its progress, it keeps generation numbers and recover bits in a dlm "control" lock lvb, which is seen by all nodes to determine which journals need to be replayed. The gfs2 on all nodes get the same recovery requests from dlm, so they all try to do the recovery, but only one will be granted the exclusive lock on the journal. The others fail with a "Busy" message on their "try lock." However, when a node is withdrawn, it cannot safely do any recovery or replay any journals. To make matters worse, gfs2 might withdraw as a result of attempting recovery. For example, this might happen if the device goes offline, or if an hba fails. But in today's gfs2 code, it doesn't check for being withdrawn at any step in the recovery process. What's worse is that these callbacks from dlm have no return code, so there is no way to indicate failure back to dlm. We can send a "Recovery failed" uevent eventually, but that tells user space what happened, not dlm's kernel code. Before this patch, lock_dlm would perform its recovery steps but ignore the result, and eventually it would still update its generation number in the lvb, despite the fact that it may have withdrawn or encountered an error. The other nodes would then see the newer generation number in the lvb and conclude that they don't need to do recovery because the generation number is newer than the last one they saw. They think a different node has already recovered the journal. This patch adds checks to several of the callbacks used by dlm in its recovery state machine so that the functions are ignored and skipped if an io error has occurred or if the file system is withdrawn. That prevents the lvb bits from being updated, and therefore dlm and user space still see the need for recovery to take place. Signed-off-by: Bob Peterson <rpeterso@redhat.com> Reviewed-by: Andreas Gruenbacher <agruenba@redhat.com> |
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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.