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Commit e611eecd authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: add comment saying why DEBUG_OBJECTS_RCU_HEAD depends on PREEMPT. 



The build will break if you change the Kconfig to allow
DEBUG_OBJECTS_RCU_HEAD and !PREEMPT, so document the reasoning
near where the breakage would occur.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent fe8e6407

kernel/rcupdate.c

+5 −0
Original line number Diff line number Diff line
@@ -214,6 +214,11 @@ static int rcuhead_fixup_free(void *addr, enum debug_obj_state state) 
		 * Ensure that queued callbacks are all executed.

		 * If we detect that we are nested in a RCU read-side critical

		 * section, we should simply fail, otherwise we would deadlock.

		 * Note that the machinery to reliably determine whether

		 * or not we are in an RCU read-side critical section

		 * exists only in the preemptible RCU implementations

		 * (TINY_PREEMPT_RCU and TREE_PREEMPT_RCU), which is why

		 * DEBUG_OBJECTS_RCU_HEAD is disallowed if !PREEMPT.

		 */

		if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||

		    irqs_disabled()) {