Patch "rcu-tasks: Remove preemption disablement around srcu_read_[un]lock() calls" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    rcu-tasks: Remove preemption disablement around srcu_read_[un]lock() calls

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     rcu-tasks-remove-preemption-disablement-around-srcu_.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit e8bc19fe6e6cbb0be238342e2cce37ea28536691
Author: Frederic Weisbecker <frederic@xxxxxxxxxx>
Date:   Fri Nov 25 14:54:59 2022 +0100

    rcu-tasks: Remove preemption disablement around srcu_read_[un]lock() calls
    
    [ Upstream commit 44757092958bdd749775022f915b7ac974384c2a ]
    
    Ever since the following commit:
    
            5a41344a3d83 ("srcu: Simplify __srcu_read_unlock() via this_cpu_dec()")
    
    SRCU doesn't rely anymore on preemption to be disabled in order to
    modify the per-CPU counter. And even then it used to be done from the API
    itself.
    
    Therefore and after checking further, it appears to be safe to remove
    the preemption disablement around __srcu_read_[un]lock() in
    exit_tasks_rcu_start() and exit_tasks_rcu_finish()
    
    Suggested-by: Boqun Feng <boqun.feng@xxxxxxxxx>
    Suggested-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
    Suggested-by: Neeraj Upadhyay <quic_neeraju@xxxxxxxxxxx>
    Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
    Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
    Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
    Stable-dep-of: 28319d6dc5e2 ("rcu-tasks: Fix synchronize_rcu_tasks() VS zap_pid_ns_processes()")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index d937bacf27b68..2408ca633872a 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -632,9 +632,7 @@ EXPORT_SYMBOL_GPL(show_rcu_tasks_classic_gp_kthread);
  */
 void exit_tasks_rcu_start(void) __acquires(&tasks_rcu_exit_srcu)
 {
-	preempt_disable();
 	current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu);
-	preempt_enable();
 }
 
 /*
@@ -646,9 +644,7 @@ void exit_tasks_rcu_finish(void) __releases(&tasks_rcu_exit_srcu)
 {
 	struct task_struct *t = current;
 
-	preempt_disable();
 	__srcu_read_unlock(&tasks_rcu_exit_srcu, t->rcu_tasks_idx);
-	preempt_enable();
 	exit_tasks_rcu_finish_trace(t);
 }