• Paul E. McKenney's avatar
    rcu: Apply RCU-bh QSes to RCU-sched and RCU-preempt when safe · d28139c4
    Paul E. McKenney authored
    One necessary step towards consolidating the three flavors of RCU is to
    make sure that the resulting consolidated "one flavor to rule them all"
    correctly handles networking denial-of-service attacks.  One thing that
    allows RCU-bh to do so is that __do_softirq() invokes rcu_bh_qs() every
    so often, and so something similar has to happen for consolidated RCU.
    This must be done carefully.  For example, if a preemption-disabled
    region of code takes an interrupt which does softirq processing before
    returning, consolidated RCU must ignore the resulting rcu_bh_qs()
    invocations -- preemption is still disabled, and that means an RCU
    reader for the consolidated flavor.
    This commit therefore creates a new rcu_softirq_qs() that is called only
    from the ksoftirqd task, thus avoiding the interrupted-a-preempted-region
    problem.  This new rcu_softirq_qs() function invokes rcu_sched_qs(),
    rcu_preempt_qs(), and rcu_preempt_deferred_qs().  The latter call handles
    any deferred quiescent states.
    Note that __do_softirq() still invokes rcu_bh_qs().  It will continue to
    do so until a later stage of cleanup when the RCU-bh flavor is removed.
    Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
    [ paulmck: Fix !SMP issue located by kbuild test robot. ]
softirq.c 18.6 KB