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The force_qs_rnp() function checks for ->qsmask being all zero, that is, all CPUs for the current rcu_node structure having already passed through quiescent states. But with RCU-preempt, this is not sufficient to report quiescent states further up the tree, so there are further checks that can initiate RCU priority boosting and also for races with CPU-hotplug operations. However, if neither of these further checks apply, the code proceeds to carry out a useless scan of an all-zero ->qsmask. This commit therefore adds code to release the current rcu_node structure's lock and continue on to the next rcu_node structure, thereby avoiding this useless scan. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.