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.
