rcu: Fix batch-limit size problem (878d7439) · Commits · 戴 / test

Commit (rcu: Add event-tracing for RCU callback invocation) added a regression in rcu_do_batch() Under stress, RCU is supposed to allow to process all items in queue, instead of a batch of 10 items (blimit), but an integer overflow makes the effective limit being 1. So, unless there is frequent idle periods (during which RCU ignores batch limits), RCU can be forced into a state where it cannot keep up with the callback-generation rate, eventually resulting in OOM. This commit therefore converts a few variables in rcu_do_batch() from int to long to fix this problem, along with the module parameters controlling the batch limits. Signed-off-by:

Eric Dumazet <edumazet@google.com> Signed-off-by:

Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: <stable@vger.kernel.org> # 3.2 +

kernel/rcutree.c

+8 −7

Original line number	Diff line number	Diff line
		@@ -212,13 +212,13 @@ DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
		#endif
		};

		static int blimit = 10; /* Maximum callbacks per rcu_do_batch. */
		static int qhimark = 10000; /* If this many pending, ignore blimit. */
		static int qlowmark = 100; /* Once only this many pending, use blimit. */
		static long blimit = 10; /* Maximum callbacks per rcu_do_batch. */
		static long qhimark = 10000; /* If this many pending, ignore blimit. */
		static long qlowmark = 100; /* Once only this many pending, use blimit. */

		module_param(blimit, int, 0444);
		module_param(qhimark, int, 0444);
		module_param(qlowmark, int, 0444);
		module_param(blimit, long, 0444);
		module_param(qhimark, long, 0444);
		module_param(qlowmark, long, 0444);

		int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
		int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
		@@ -1791,7 +1791,8 @@ static void rcu_do_batch(struct rcu_state rsp, struct rcu_data rdp)
		{
		unsigned long flags;
		struct rcu_head next, list, **tail;
		int bl, count, count_lazy, i;
		long bl, count, count_lazy;
		int i;

		/* If no callbacks are ready, just return.*/
		if (!cpu_has_callbacks_ready_to_invoke(rdp)) {

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