e4453d8a1c
The scheduler is currently required to hold rq/pi locks across the entire RCU read-side critical section or not at all. This is inconvenient and leaves traps for the unwary, including the author of this commit. But now that excessively long grace periods enable scheduling-clock interrupts for holdout nohz_full CPUs, the nohz_full rescue logic in rcu_read_unlock_special() can be dispensed with. In other words, the rcu_read_unlock_special() function can refrain from doing wakeups unless such wakeups are guaranteed safe. This commit therefore avoids unsafe wakeups, freeing the scheduler to hold rq/pi locks across rcu_read_unlock() even if the corresponding RCU read-side critical section might have been preempted. This commit also updates RCU's requirements documentation. This commit is inspired by a patch from Lai Jiangshan: https://lore.kernel.org/lkml/20191102124559.1135-2-laijs@linux.alibaba.com This commit is further intended to be a step towards his goal of permitting the inlining of RCU-preempt's rcu_read_lock() and rcu_read_unlock(). Cc: Lai Jiangshan <laijs@linux.alibaba.com> 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.