From: "Paul E. McKenney" paulmck@kernel.org
[ 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@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 Stable-dep-of: 876673364161 ("bpf: Defer the free of inner map when necessary") Signed-off-by: Sasha Levin sashal@kernel.org (cherry picked from commit 10108826191ab30388e8ae9d54505a628f78a7ec) Signed-off-by: Robert Kolchmeyer rkolchmeyer@google.com --- include/linux/rcupdate.h | 12 ++++++++++++ kernel/rcu/tasks.h | 2 ++ 2 files changed, 14 insertions(+)
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 13bddb841ceb..e3b12de36e92 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -205,6 +205,18 @@ 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 28f628c70245..b24ef77325ee 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -1098,6 +1098,8 @@ 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_reader_checked. }