[PATCH v2 22/45] percpu_counter: Use get/put_online_cpus_atomic() to prevent CPU offline
From: Srivatsa S. Bhat <hidden>
Date: 2013-06-25 20:33:15
Also in:
linux-arch, linuxppc-dev, lkml, netdev
Subsystem:
library code, per-cpu memory allocator, the rest · Maintainers:
Andrew Morton, Dennis Zhou, Tejun Heo, Christoph Lameter, Linus Torvalds
Once stop_machine() is gone from the CPU offline path, we won't be able to depend on disabling preemption to prevent CPUs from going offline from under us. Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going offline, while invoking from atomic context. Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Tejun Heo <tj@kernel.org> Signed-off-by: Srivatsa S. Bhat <redacted> --- lib/percpu_counter.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index ba6085d..f5e718d 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c@@ -98,6 +98,15 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc) s64 ret; int cpu; + /* + * The calls to get/put_online_cpus_atomic() is strictly not + * necessary, since CPU hotplug is explicitly handled via the + * hotplug callback which synchronizes through fbc->lock. + * But we add them here anyway to make it easier for the debug + * code under CONFIG_DEBUG_HOTPLUG_CPU to validate the correctness + * of hotplug synchronization. + */ + get_online_cpus_atomic(); raw_spin_lock(&fbc->lock); ret = fbc->count; for_each_online_cpu(cpu) {
@@ -105,6 +114,7 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc) ret += *pcount; } raw_spin_unlock(&fbc->lock); + put_online_cpus_atomic(); return ret; } EXPORT_SYMBOL(__percpu_counter_sum);