Re: [PATCH] checkpatch: Remove migrated RCU APIs from deprecated_apis
From: Paul E. McKenney
Date: Thu Jan 09 2025 - 12:01:40 EST
On Thu, Jan 09, 2025 at 07:56:51AM -0800, Joe Perches wrote:
> On Wed, 2025-01-08 at 11:24 -0800, David Reaver wrote:
> > The deprecated_apis map was created in [1] so checkpatch would flag
> > deprecated RCU APIs. These deprecated APIs have since been removed from the
> > kernel. This patch removes them from this map so checkpatch doesn't waste
> > time looking for them, and so readers of checkpatch looking for deprecated
> > APIs don't waste time searching for them.
>
> Acked-by: Joe Perches <joe@xxxxxxxxxxx>
>
> Maybe remove the references from rcupdateup.h one day too.
Good point, please see below.
Some instances remain in Documentation/RCU/RTFP.txt, but these are needed
to record the history.
Thanx, Paul
------------------------------------------------------------------------
commit a8280286a6425f26785aeedfe9b209a65ca1d6fd
Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
Date: Thu Jan 9 08:52:15 2025 -0800
rcu: Remove references to old grace-period-wait primitives
The rcu_barrier_sched(), synchronize_sched(), and synchronize_rcu_bh()
RCU API members have been gone for many years. This commit therefore
removes non-historical instances of them.
Reported-by: Joe Perches <joe@xxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
diff --git a/Documentation/RCU/rcubarrier.rst b/Documentation/RCU/rcubarrier.rst
index 6da7f66da2a80..12a7b059654f7 100644
--- a/Documentation/RCU/rcubarrier.rst
+++ b/Documentation/RCU/rcubarrier.rst
@@ -329,10 +329,7 @@ Answer:
was first added back in 2005. This is because on_each_cpu()
disables preemption, which acted as an RCU read-side critical
section, thus preventing CPU 0's grace period from completing
- until on_each_cpu() had dealt with all of the CPUs. However,
- with the advent of preemptible RCU, rcu_barrier() no longer
- waited on nonpreemptible regions of code in preemptible kernels,
- that being the job of the new rcu_barrier_sched() function.
+ until on_each_cpu() had dealt with all of the CPUs.
However, with the RCU flavor consolidation around v4.20, this
possibility was once again ruled out, because the consolidated
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 6672e55deeaa4..9b05db8ff0619 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -800,11 +800,9 @@ do { \
* sections, invocation of the corresponding RCU callback is deferred
* until after the all the other CPUs exit their critical sections.
*
- * In v5.0 and later kernels, synchronize_rcu() and call_rcu() also
- * wait for regions of code with preemption disabled, including regions of
- * code with interrupts or softirqs disabled. In pre-v5.0 kernels, which
- * define synchronize_sched(), only code enclosed within rcu_read_lock()
- * and rcu_read_unlock() are guaranteed to be waited for.
+ * Both synchronize_rcu() and call_rcu() also wait for regions of code
+ * with preemption disabled, including regions of code with interrupts or
+ * softirqs disabled.
*
* Note, however, that RCU callbacks are permitted to run concurrently
* with new RCU read-side critical sections. One way that this can happen
@@ -859,11 +857,10 @@ static __always_inline void rcu_read_lock(void)
* rcu_read_unlock() - marks the end of an RCU read-side critical section.
*
* In almost all situations, rcu_read_unlock() is immune from deadlock.
- * In recent kernels that have consolidated synchronize_sched() and
- * synchronize_rcu_bh() into synchronize_rcu(), this deadlock immunity
- * also extends to the scheduler's runqueue and priority-inheritance
- * spinlocks, courtesy of the quiescent-state deferral that is carried
- * out when rcu_read_unlock() is invoked with interrupts disabled.
+ * This deadlock immunity also extends to the scheduler's runqueue
+ * and priority-inheritance spinlocks, courtesy of the quiescent-state
+ * deferral that is carried out when rcu_read_unlock() is invoked with
+ * interrupts disabled.
*
* See rcu_read_lock() for more information.
*/