• Paul E. McKenney's avatar
    rcu: Complain if blocking in preemptible RCU read-side critical section · 5b72f964
    Paul E. McKenney authored
    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: default avatarThomas Gleixner <tglx@linutronix.de>
    Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
    5b72f964
tree_plugin.h 87.5 KB