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Date: Fri, 4 Jan 2008 17:39:05 +0530 From: Gautham R Shenoy <ego@...ibm.com> To: Paul E McKenney <paulmck@...ibm.com>, Steven Rostedt <rostedt@...dmis.org> Cc: "K. Prasad" <prasad@...ux.vnet.ibm.com>, mingo@...e.hu, linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org, dipankar@...ibm.com, Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> Subject: __get_cpu_var() called from a preempt-unsafe context in __rcu_preempt_unboost() ? Hi Paul, Steve, This is with reference to the preemptible rcu implementation in 2.6.24-rc5-rt1. In __rcu_read_unlock(), we call __rcu_preempt_unboost() to unboost a task's priority which had been bumped up when it was preempted out while the rcu_read section. The code path is as follows __rcu_read_unlock() | |--> local_irq_restore(oldirq); | |--> __rcu_preempt_unboost(); | |--> rcu_trace_boost_unboost_called(RCU_BOOST_ME) where RCU_BOOST_ME is #defined as &__get_cpu_var(rcu_boost_data). Is calling __get_cpu_var() safe in this context, since we've already enabled the local interrupts and we're not in a preempt_disabled() ? Thanks and Regards gautham. -- Gautham R Shenoy Linux Technology Center IBM India. "Freedom comes with a price tag of responsibility, which is still a bargain, because Freedom is priceless!" -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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