Patch "rcu-tasks: Provide rcu_trace_implies_rcu_gp()" has been added to the 6.1-stable tree

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

    rcu-tasks: Provide rcu_trace_implies_rcu_gp()

to the 6.1-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-provide-rcu_trace_implies_rcu_gp.patch
and it can be found in the queue-6.1 subdirectory.

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



commit fd1ee3524bbdf475d958a20360dca83b307fe1d1
Author: Paul E. McKenney <paulmck@xxxxxxxxxx>
Date:   Fri Oct 14 19:39:43 2022 +0800

    rcu-tasks: Provide rcu_trace_implies_rcu_gp()
    
    [ Upstream commit e6c86c513f440bec5f1046539c7e3c6c653842da ]
    
    As an accident of implementation, an RCU Tasks Trace grace period also
    acts as an RCU grace period.  However, this could change at any time.
    This commit therefore creates an rcu_trace_implies_rcu_gp() that currently
    returns true to codify this accident.  Code relying on this accident
    must call this function to verify that this accident is still happening.
    
    Reported-by: Hou Tao <houtao@xxxxxxxxxxxxxxx>
    Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
    Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
    Cc: Martin KaFai Lau <martin.lau@xxxxxxxxx>
    Link: https://lore.kernel.org/r/20221014113946.965131-2-houtao@xxxxxxxxxxxxxxx
    Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
    Stable-dep-of: 876673364161 ("bpf: Defer the free of inner map when necessary")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index e9e61cd27ef6..46bd9a331fd5 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -242,6 +242,18 @@ static inline void exit_tasks_rcu_stop(void) { }
 static inline void exit_tasks_rcu_finish(void) { }
 #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */
 
+/**
+ * rcu_trace_implies_rcu_gp - does an RCU Tasks Trace grace period imply an RCU grace period?
+ *
+ * As an accident of implementation, an RCU Tasks Trace grace period also
+ * acts as an RCU grace period.  However, this could change at any time.
+ * Code relying on this accident must call this function to verify that
+ * this accident is still happening.
+ *
+ * You have been warned!
+ */
+static inline bool rcu_trace_implies_rcu_gp(void) { return true; }
+
 /**
  * cond_resched_tasks_rcu_qs - Report potential quiescent states to RCU
  *
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index c1f18c63b9b1..b5d5b6cf093a 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1570,6 +1570,8 @@ static void rcu_tasks_trace_postscan(struct list_head *hop)
 {
 	// Wait for late-stage exiting tasks to finish exiting.
 	// These might have passed the call to exit_tasks_rcu_finish().
+
+	// If you remove the following line, update rcu_trace_implies_rcu_gp()!!!
 	synchronize_rcu();
 	// Any tasks that exit after this point will set
 	// TRC_NEED_QS_CHECKED in ->trc_reader_special.b.need_qs.




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