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While reporting a quiescent state for a given CPU, rcu_core() takes advantage of the freshly loaded grace period sequence number and the locked rnp to accelerate the callbacks whose sequence number have been assigned a stale value. This action is only necessary when the rdp isn't offloaded, otherwise the NOCB kthreads already take care of the callbacks progression. However the check for the offloaded state is volatile because it is performed outside the IRQs disabled section. It's possible for the offloading process to preempt rcu_core() at that point on PREEMPT_RT. This is dangerous because rcu_core() may end up accelerating callbacks concurrently with NOCB kthreads without appropriate locking. Fix this with moving the offloaded check inside the rnp locking section. Reported-and-tested-by: Valentin Schneider <valentin.schneider@arm.com> Reviewed-by: Valentin Schneider <valentin.schneider@arm.com> Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Joel Fernandes <joel@joelfernandes.org> Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Neeraj Upadhyay <neeraju@codeaurora.org> Cc: Uladzislau Rezki <urezki@gmail.com> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Frederic Weisbecker <frederic@kernel.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.