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Currently, rcu_cpu_starting() checks to see if the RCU core expects a quiescent state from the incoming CPU. However, the current interaction between RCU quiescent-state reporting and CPU-hotplug operations should mean that the incoming CPU never needs to report a quiescent state. First, the outgoing CPU reports a quiescent state if needed. Second, the race where the CPU is leaving just as RCU is initializing a new grace period is handled by an explicit check for this condition. Third, the CPU's leaf rcu_node structure's ->lock serializes these checks. This means that if rcu_cpu_starting() ever feels the need to report a quiescent state, then there is a bug somewhere in the CPU hotplug code or the RCU grace-period handling code. This commit therefore adds a WARN_ON_ONCE() to bring that bug to everyone's attention. Cc: Neeraj Upadhyay <neeraju@codeaurora.org> Suggested-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.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.