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A full memory barrier in the RCU-PREEMPT task unblock path advertizes to order the context switch (or rather the accesses prior to rcu_read_unlock()) with the expedited grace period fastpath. However the grace period can not complete without the rnp calling into rcu_report_exp_rnp() with the node locked. This reports the quiescent state in a fully ordered fashion against updater's accesses thanks to: 1) The READ-SIDE smp_mb__after_unlock_lock() barrier across nodes locking while propagating QS up to the root. 2) The UPDATE-SIDE smp_mb__after_unlock_lock() barrier while holding the the root rnp to wait/check for the GP completion. 3) The (perhaps redundant given step 1) and 2)) smp_mb() in rcu_seq_end() before the grace period completes. This makes the explicit barrier in this place superfluous. Therefore remove it as it is confusing. Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com> Signed-off-by: Neeraj Upadhyay (AMD) <neeraj.upadhyay@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 reStructuredText 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.