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With Ankur's lazy-/auto-preemption patches applied and with a lazy-preemptible kernel in combination with a non-preemptible RCU, lockdep sometimes complains about context switches within RCU read-side critical sections. This is a false positive due to rcu_read_unlock() updating lockdep state too late: __release(RCU); __rcu_read_unlock(); // Context switch here results in lockdep false positive!!! rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */ Although this complaint could also happen with preemptible RCU in a preemptible kernel, the odds of that happening aer quite low. In constrast, with non-preemptible RCU, a long critical section has a high probability of performing a context switch from the preempt_enable() in __rcu_read_unlock(). The fix is straightforward, just move the rcu_lock_release() within rcu_read_unlock() to obtain the reverse order from that of rcu_read_lock(): rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */ __release(RCU); __rcu_read_unlock(); This commit makes this change. Co-developed-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Co-developed-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Co-developed-by: Boqun Feng <boqun.feng@gmail.com> Signed-off-by: Boqun Feng <boqun.feng@gmail.com> Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com> Reviewed-by: Paul E. McKenney <paulmck@kernel.org> Cc: Ankur Arora <ankur.a.arora@oracle.com> Cc: Thomas Gleixner <tglx@linutronix.de>
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.