lkml.org 
[lkml]   [2017]   [Apr]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH tip/core/rcu 08/40] rcu: Make call_rcu() do deferred NOCB wakeups
    Date
    If a CONFIG_RCU_NOCB_CPUS kernel invokes call_rcu() with interrupts
    disabled, wakeups must be deferred in order to avoid self-deadlock in the
    cases where the disabled interrupts are due to scheduler locks being held.
    In this case, a flag is set and is checked on entry to extended quiescent
    states (usermode, idle), on exit from the RCU_SOFTIRQ handler, and when
    the CPU in question goes offline. However, a given CPU could avoid all
    of those states for a considerable length of time.

    This commit therefore allows a subsequent invocation of call_rcu() with
    interrupts enabled to do the wakeup. It also makes the wakeup function
    clear the deferred-wakeup flag.

    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    ---
    kernel/rcu/tree_plugin.h | 5 ++++-
    1 file changed, 4 insertions(+), 1 deletion(-)

    diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
    index 0a62a8f1caac..5a149091d262 100644
    --- a/kernel/rcu/tree_plugin.h
    +++ b/kernel/rcu/tree_plugin.h
    @@ -1768,6 +1768,7 @@ static void wake_nocb_leader(struct rcu_data *rdp, bool force)
    return;
    if (READ_ONCE(rdp_leader->nocb_leader_sleep) || force) {
    /* Prior smp_mb__after_atomic() orders against prior enqueue. */
    + WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOGP_WAKE_NOT);
    WRITE_ONCE(rdp_leader->nocb_leader_sleep, false);
    swake_up(&rdp_leader->nocb_wq);
    }
    @@ -1853,7 +1854,9 @@ static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
    return;
    }
    len = atomic_long_read(&rdp->nocb_q_count);
    - if (old_rhpp == &rdp->nocb_head) {
    + if (old_rhpp == &rdp->nocb_head ||
    + (rcu_nocb_need_deferred_wakeup(rdp) &&
    + !irqs_disabled_flags(flags))) {
    if (!irqs_disabled_flags(flags)) {
    /* ... if queue was empty ... */
    wake_nocb_leader(rdp, false);
    --
    2.5.2
    \
     
     \ /
      Last update: 2017-04-12 19:41    [W:4.062 / U:0.020 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site