rcu: Add Kconfig option for strict RCU grace periods (8cbd0e38) · Commits · 戴 / test

People running automated tests have asked for a way to make RCU minimize grace-period duration in order to increase the probability of KASAN detecting a pointer being improperly leaked from an RCU read-side critical section, for example, like this: rcu_read_lock(); p = rcu_dereference(gp); do_something_with(p); // OK rcu_read_unlock(); do_something_else_with(p); // BUG!!! The rcupdate.rcu_expedited boot parameter is a start in this direction, given that it makes calls to synchronize_rcu() instead invoke the faster (and more wasteful) synchronize_rcu_expedited(). However, this does nothing to shorten RCU grace periods that are instead initiated by call_rcu(), and RCU pointer-leak bugs can involve call_rcu() just as surely as they can synchronize_rcu(). This commit therefore adds a RCU_STRICT_GRACE_PERIOD Kconfig option that will be used to shorten normal (non-expedited) RCU grace periods. This commit also dumps out a message when this option is in effect. Later commits will actually shorten grace periods. Reported-by Jann Horn <jannh@google.com> Signed-off-by:

Paul E. McKenney <paulmck@kernel.org>

kernel/rcu/Kconfig.debug

+15 −0

Original line number	Diff line number	Diff line
		@@ -114,4 +114,19 @@ config RCU_EQS_DEBUG
		Say N here if you need ultimate kernel/user switch latencies
		Say Y if you are unsure

		config RCU_STRICT_GRACE_PERIOD
		bool "Provide debug RCU implementation with short grace periods"
		depends on DEBUG_KERNEL && RCU_EXPERT
		default n
		select PREEMPT_COUNT if PREEMPT=n
		help
		Select this option to build an RCU variant that is strict about
		grace periods, making them as short as it can. This limits
		scalability, destroys real-time response, degrades battery
		lifetime and kills performance. Don't try this on large
		machines, as in systems with more than about 10 or 20 CPUs.
		But in conjunction with tools like KASAN, it can be helpful
		when looking for certain types of RCU usage bugs, for example,
		too-short RCU read-side critical sections.

		endmenu # "RCU Debugging"

kernel/rcu/tree_plugin.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -36,6 +36,8 @@ static void __init rcu_bootup_announce_oddness(void)
		pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
		if (IS_ENABLED(CONFIG_PROVE_RCU))
		pr_info("\tRCU lockdep checking is enabled.\n");
		if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
		pr_info("\tRCU strict (and thus non-scalable) grace periods enabled.\n");
		if (RCU_NUM_LVLS >= 4)
		pr_info("\tFour(or more)-level hierarchy is enabled.\n");
		if (RCU_FANOUT_LEAF != 16)

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