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Current submission path has no way to restrict the submitter from stop submiting on shutdown path or wq disable path. This provides a way to quiesce the submission path. Modeling after 'struct reqeust_queue' usage of percpu_ref. One of the abilities of per_cpu reference counting is the ability to stop new references from being taken while awaiting outstanding references to be dropped. On wq shutdown, we want to block any new submissions to the kernel workqueue and quiesce before disabling. The percpu_ref allows us to block any new submissions and wait for any current submission calls to finish submitting to the workqueue. A percpu_ref is embedded in each idxd_wq context to allow control for individual wq. The wq->wq_active counter is elevated before calling movdir64b() or enqcmds() to submit a descriptor to the wq and dropped once the submission call completes. The function is gated by percpu_ref_tryget_live(). On shutdown with percpu_ref_kill() called, any new submission would be blocked from acquiring a ref and failed. Once all references are dropped for the wq, shutdown can continue. Signed-off-by: Dave Jiang <dave.jiang@intel.com> Link: https://lore.kernel.org/r/161894438293.3202472.14894701611500822232.stgit@djiang5-desk3.ch.intel.com Signed-off-by: Vinod Koul <vkoul@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.