From: "Paul E. McKenney" <paulmck@kernel.org>
Date: Fri, 14 Oct 2022 19:39:43 +0800
Subject: rcu-tasks: Provide rcu_trace_implies_rcu_gp()
Patch-mainline: v6.2-rc1
Git-commit: e6c86c513f440bec5f1046539c7e3c6c653842da
References: bsc#1220251 CVE-2023-52447
X-Info: dependency of patches.suse/bpf-Defer-the-free-of-inner-map-when-necessary.patch with no behavior change

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@huaweicloud.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Link: https://lore.kernel.org/r/20221014113946.965131-2-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 include/linux/rcupdate.h |   12 ++++++++++++
 kernel/rcu/tasks.h       |    2 ++
 2 files changed, 14 insertions(+)

--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -204,6 +204,18 @@ static inline void exit_tasks_rcu_finish
 #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
  *
  * This macro resembles cond_resched(), except that it is defined to
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1071,6 +1071,8 @@ static void rcu_tasks_trace_postscan(str
 
 	// 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_reader_checked.
 }