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It makes no sense to de-offload an offline CPU because that CPU will never invoke any remaining callbacks. It also makes little sense to offload an offline CPU because any pending RCU callbacks were migrated when that CPU went offline. Yes, it is in theory possible to use a number of tricks to permit offloading and deoffloading offline CPUs in certain cases, but in practice it is far better to have the simple and deterministic rule "Toggling the offload state of an offline CPU is forbidden". For but one example, consider that an offloaded offline CPU might have millions of callbacks queued. Best to just say "no". This commit therefore forbids toggling of the offloaded state of offline CPUs. Reported-by: Paul E. McKenney <paulmck@kernel.org> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Joel Fernandes <joel@joelfernandes.org> Cc: Neeraj Upadhyay <neeraju@codeaurora.org> Cc: Boqun Feng <boqun.feng@gmail.com> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@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.