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rcu: Remove _rcu_barrier() dependency on __stop_machine()

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Currently, _rcu_barrier() relies on preempt_disable() to prevent
any CPU from going offline, which in turn depends on CPU hotplug's
use of __stop_machine().

This patch therefore makes _rcu_barrier() use get_online_cpus() to
block CPU-hotplug operations.  This has the added benefit of removing
the need for _rcu_barrier() to adopt callbacks:  Because CPU-hotplug
operations are excluded, there can be no callbacks to adopt.  This
commit simplifies the code accordingly.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
This commit is contained in:
Paul E. McKenney
2012-08-02 17:43:50 -07:00
committed by Paul E. McKenney
parent a10d206ef1
commit 1331e7a1bb
3 changed files with 13 additions and 77 deletions
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4
kernel/rcutree_trace.c
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@@ -51,8 +51,8 @@ static int show_rcubarrier(struct seq_file *m, void *unused)
struct rcu_state *rsp;
for_each_rcu_flavor(rsp)
seq_printf(m, "%s: %c bcc: %d nbd: %lu\n",
rsp->name, rsp->rcu_barrier_in_progress ? 'B' : '.',
seq_printf(m, "%s: bcc: %d nbd: %lu\n",
rsp->name,
atomic_read(&rsp->barrier_cpu_count),
rsp->n_barrier_done);
return 0;