Commit 6ca0292c authored Jul 01, 2022 by Zqiang Committed by Paul E. McKenney Aug 31, 2022

rcu: Make tiny RCU support leak callbacks for debug-object errors



Currently, only Tree RCU leaks callbacks setting when it detects a
duplicate call_rcu().  This commit causes Tiny RCU to also leak
callbacks in this situation.

Because this is Tiny RCU, kernel size is important:

1. CONFIG_TINY_RCU=y and CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
   (Production kernel)

    Original:
    text      data      bss       dec       hex     filename
    26290663  20159823  15212544  61663030  3ace736 vmlinux

    With this commit:
    text      data      bss       dec       hex     filename
    26290663  20159823  15212544  61663030  3ace736 vmlinux

2. CONFIG_TINY_RCU=y and CONFIG_DEBUG_OBJECTS_RCU_HEAD=y
   (Debugging kernel)

    Original:
    text      data      bss       dec       hex     filename
    26291319  20160143  15212544  61664006  3aceb06 vmlinux

    With this commit:
    text      data      bss       dec       hex     filename
    26291319  20160431  15212544  61664294  3acec26 vmlinux

These results show that the kernel size is unchanged for production
kernels, as desired.

Signed-off-by: Zqiang <qiang1.zhang@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

parent fcb42c9a

kernel/rcu/tiny.c

+16 −1

Original line number	Diff line number	Diff line
		@@ -158,6 +158,10 @@ void synchronize_rcu(void)
		}
		EXPORT_SYMBOL_GPL(synchronize_rcu);

		static void tiny_rcu_leak_callback(struct rcu_head *rhp)
		{
		}

		/*
		* Post an RCU callback to be invoked after the end of an RCU grace
		* period. But since we have but one CPU, that would be after any
		@@ -165,9 +169,20 @@ EXPORT_SYMBOL_GPL(synchronize_rcu);
		*/
		void call_rcu(struct rcu_head *head, rcu_callback_t func)
		{
		static atomic_t doublefrees;
		unsigned long flags;

		debug_rcu_head_queue(head);
		if (debug_rcu_head_queue(head)) {
		if (atomic_inc_return(&doublefrees) < 4) {
		pr_err("%s(): Double-freed CB %p->%pS()!!! ", __func__, head, head->func);
		mem_dump_obj(head);
		}

		if (!__is_kvfree_rcu_offset((unsigned long)head->func))
		WRITE_ONCE(head->func, tiny_rcu_leak_callback);
		return;
		}

		head->func = func;
		head->next = NULL;