From 79a62f957e0b37c59610a96d018cc341aebb48f4 Mon Sep 17 00:00:00 2001 From: Lai Jiangshan Date: Wed, 30 Oct 2013 04:13:22 -0700 Subject: [PATCH] rcu: Warn on allegedly impossible rcu_read_unlock_special() from irq After commit #10f39bb1b2c1 (rcu: protect __rcu_read_unlock() against scheduler-using irq handlers), it is no longer possible to enter the main body of rcu_read_lock_special() from an NMI, interrupt, or softirq handler. In theory, this implies that the check for "in_irq() || in_serving_softirq()" must always fail, so that in theory this check could be removed entirely. In practice, this commit wraps this condition with a WARN_ON_ONCE(). If this warning never triggers, then the condition will be removed entirely. [ paulmck: And one way of triggering the WARN_ON() is if a scheduling clock interrupt occurs in an RCU read-side critical section, setting RCU_READ_UNLOCK_NEED_QS, which is handled by rcu_read_unlock_special(). Updated this commit to return if only that bit was set. ] Signed-off-by: Lai Jiangshan Signed-off-by: Paul E. McKenney --- Reading git-format-patch failed