Commit 90326f05 authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Paul E. McKenney
Browse files

rcu: Use CONFIG_PREEMPTION where appropriate 



The config option `CONFIG_PREEMPT' is used for the preemption model
"Low-Latency Desktop". The config option `CONFIG_PREEMPTION' is enabled
when kernel preemption is enabled which is true for the preemption model
`CONFIG_PREEMPT' and `CONFIG_PREEMPT_RT'.

Use `CONFIG_PREEMPTION' if it applies to both preemption models and not
just to `CONFIG_PREEMPT'.

Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: rcu@vger.kernel.org
Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent b3e627d3

include/linux/rcupdate.h

+2 −2
Original line number Diff line number Diff line
@@ -154,7 +154,7 @@ static inline void exit_tasks_rcu_finish(void) { } 
 *

 * This macro resembles cond_resched(), except that it is defined to

 * report potential quiescent states to RCU-tasks even if the cond_resched()

 * machinery were to be shut off, as some advocate for PREEMPT kernels.

 * machinery were to be shut off, as some advocate for PREEMPTION kernels.

 */

#define cond_resched_tasks_rcu_qs() \

do { \
@@ -598,7 +598,7 @@ do { \ 
 *

 * You can avoid reading and understanding the next paragraph by

 * following this rule: don't put anything in an rcu_read_lock() RCU

 * read-side critical section that would block in a !PREEMPT kernel.

 * read-side critical section that would block in a !PREEMPTION kernel.

 * But if you want the full story, read on!

 *

 * In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU),

kernel/rcu/Kconfig

+2 −2
Original line number Diff line number Diff line
@@ -201,8 +201,8 @@ config RCU_NOCB_CPU 
	  specified at boot time by the rcu_nocbs parameter.  For each

	  such CPU, a kthread ("rcuox/N") will be created to invoke

	  callbacks, where the "N" is the CPU being offloaded, and where

	  the "p" for RCU-preempt (PREEMPT kernels) and "s" for RCU-sched

	  (!PREEMPT kernels).  Nothing prevents this kthread from running

	  the "p" for RCU-preempt (PREEMPTION kernels) and "s" for RCU-sched

	  (!PREEMPTION kernels).  Nothing prevents this kthread from running

	  on the specified CPUs, but (1) the kthreads may be preempted

	  between each callback, and (2) affinity or cgroups can be used

	  to force the kthreads to run on whatever set of CPUs is desired.

kernel/rcu/rcutorture.c

+1 −1
Original line number Diff line number Diff line
@@ -1730,7 +1730,7 @@ static void rcu_torture_fwd_cb_cr(struct rcu_head *rhp) 
// Give the scheduler a chance, even on nohz_full CPUs.

static void rcu_torture_fwd_prog_cond_resched(unsigned long iter)

{

	if (IS_ENABLED(CONFIG_PREEMPT) && IS_ENABLED(CONFIG_NO_HZ_FULL)) {

	if (IS_ENABLED(CONFIG_PREEMPTION) && IS_ENABLED(CONFIG_NO_HZ_FULL)) {

		// Real call_rcu() floods hit userspace, so emulate that.

		if (need_resched() || (iter & 0xfff))

			schedule();

kernel/rcu/srcutiny.c

+1 −1
Original line number Diff line number Diff line
@@ -103,7 +103,7 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock); 


/*

 * Workqueue handler to drive one grace period and invoke any callbacks

 * that become ready as a result.  Single-CPU and !PREEMPT operation

 * that become ready as a result.  Single-CPU and !PREEMPTION operation

 * means that we get away with murder on synchronization.  ;-)

 */

void srcu_drive_gp(struct work_struct *wp)

kernel/rcu/tree.c

+2 −2
Original line number Diff line number Diff line
@@ -2698,9 +2698,9 @@ EXPORT_SYMBOL_GPL(kfree_call_rcu); 


/*

 * During early boot, any blocking grace-period wait automatically

 * implies a grace period.  Later on, this is never the case for PREEMPT.

 * implies a grace period.  Later on, this is never the case for PREEMPTION.

 *

 * Howevr, because a context switch is a grace period for !PREEMPT, any

 * Howevr, because a context switch is a grace period for !PREEMPTION, any

 * blocking grace-period wait automatically implies a grace period if

 * there is only one CPU online at any point time during execution of

 * either synchronize_rcu() or synchronize_rcu_expedited().  It is OK to

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