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In normal operation, the XFS convention is to take an inode's iolock and then allocate a transaction. However, when scrubbing parent inodes this is inverted -- we allocated the transaction to do the scrub, and now we're trying to grab the parent's iolock. This can lead to ABBA deadlocks: some thread grabbed the parent's iolock and is waiting for space for a transaction while our parent scrubber is sitting on a transaction trying to get the parent's iolock. Therefore, convert all iolock attempts to use trylock; if that fails, they can use the existing mechanisms to back off and try again. The ABBA deadlock didn't happen with a non-repair scrub because the transactions don't reserve any space, but repair scrubs require reservation in order to update metadata. However, any other concurrent metadata update (e.g. directory create in the parent) could also induce this deadlock with the parent scrubber. Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> Reviewed-by: Brian Foster <bfoster@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.
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.