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Although preemptible RCU allows its read-side critical sections to be preempted, general blocking is forbidden. The reason for this is that excessive preemption times can be handled by CONFIG_RCU_BOOST=y, but a voluntarily blocked task doesn't care how high you boost its priority. Because preemptible RCU is a global mechanism, one ill-behaved reader hurts everyone. Hence the prohibition against general blocking in RCU-preempt read-side critical sections. Preemption yes, blocking no. This commit enforces this prohibition. There is a special exception for the -rt patchset (which they kindly volunteered to implement): It is OK to block (as opposed to merely being preempted) within an RCU-preempt read-side critical section, but only if the blocking is subject to priority inheritance. This exception permits CONFIG_RCU_BOOST=y to get -rt RCU readers out of trouble. Why doesn't this exception also apply to mainline's rt_mutex? Because of the possibility that someone does general blocking while holding an rt_mutex. Yes, the priority boosting will affect the rt_mutex, but it won't help with the task doing general blocking while holding that rt_mutex. Reported-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> |
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| .. | ||
| Makefile | ||
| rcu_segcblist.c | ||
| rcu_segcblist.h | ||
| rcu.h | ||
| rcuperf.c | ||
| rcutorture.c | ||
| srcu.c | ||
| srcutiny.c | ||
| srcutree.c | ||
| sync.c | ||
| tiny_plugin.h | ||
| tiny.c | ||
| tree_exp.h | ||
| tree_plugin.h | ||
| tree_trace.c | ||
| tree.c | ||
| tree.h | ||
| update.c | ||