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ec711bc12c
At the start of a CPU-hotplug operation, the incoming CPU's callback list can be in a number of states: 1. Disabled and empty. This is the case when the boot CPU has not invoked call_rcu(), when a non-boot CPU first comes online, and when a non-offloaded CPU comes back online. In this case, it is both necessary and permissible to initialize ->cblist. Because either the CPU is currently running with interrupts disabled (boot CPU) or is not yet running at all (other CPUs), it is not necessary to acquire ->nocb_lock. In this case, initialization is required. 2. Disabled and non-empty. This cannot occur, because early boot call_rcu() invocations enable the callback list before enqueuing their callback. 3. Enabled, whether empty or not. In this case, the callback list has already been initialized. This case occurs when the boot CPU has executed an early boot call_rcu() and also when an offloaded CPU comes back online. In both cases, there is no need to initialize the callback list: In the boot-CPU case, the CPU has not (yet) gone offline, and in the offloaded case, the rcuo kthreads are taking care of business. Because it is not necessary to initialize the callback list, it is also not necessary to acquire ->nocb_lock. Therefore, checking if the segcblist is enabled suffices. This commit therefore initializes the callback list at rcutree_prepare_cpu() time only if that list is disabled. Signed-off-by: Frederic Weisbecker <frederic@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: Paul E. McKenney <paulmck@kernel.org> |
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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.