From: Hugh Dickins Date: Fri, 17 Feb 2012 21:20:31 +0000 (-0800) Subject: rcu: Stop spurious warnings from synchronize_sched_expedited X-Git-Tag: v3.4-rc1~194^2^2 X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=commitdiff_plain;h=1cc85961e214773cb7d7f2ccbe3bc644dd466df0;p=linux.git rcu: Stop spurious warnings from synchronize_sched_expedited synchronize_sched_expedited() is spamming CONFIG_DEBUG_PREEMPT=y users with an unintended warning from the cpu_is_offline() check: use raw_smp_processor_id() instead of smp_processor_id() there. Because the warning is under a get_online_cpus(), it is not possible for any CPUs to go offline, though it is quite possible that the task might migrate between the raw_smp_processor_id() and the check of cpu_is_offline(). This is not a problem because the task cannot migrate from an offline CPU to an online one or vice versa. The point of the check is to verify that synchronize_sched_expedited() is not called from an offline CPU, for example, from a CPU_DYING notifier, or, more important, from an outgoing CPU making its way from its CPU_DYING notifiers to the idle loop. Signed-off-by: Hugh Dickins Signed-off-by: Paul E. McKenney --- diff --git a/kernel/rcutree.c b/kernel/rcutree.c index eacc10b03531..1050d6d3922c 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -2014,7 +2014,7 @@ void synchronize_sched_expedited(void) /* Note that atomic_inc_return() implies full memory barrier. */ firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started); get_online_cpus(); - WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); + WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id())); /* * Each pass through the following loop attempts to force a