aboutsummaryrefslogtreecommitdiffstats
path: root/kernel/cpu.c
diff options
context:
space:
mode:
authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-10-22 14:51:49 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-11-03 19:21:01 -0800
commit62db99f4783ea34531fc344bd8c539d5d186f24d (patch)
tree71b90af82e70ea33e05455bf1e6d93cec77ea79e /kernel/cpu.c
parent8fa7845df539105a8962c3173c866483da74ff6d (diff)
cpu: Avoid puts_pending overflow
A long string of get_online_cpus() with each followed by a put_online_cpu() that fails to acquire cpu_hotplug.lock can result in overflow of the cpu_hotplug.puts_pending counter. Although this is perhaps improbably, a system with absolutely no CPU-hotplug operations will have an arbitrarily long time in which this overflow could occur. This commit therefore adds overflow checks to get_online_cpus() and try_get_online_cpus(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>
Diffstat (limited to 'kernel/cpu.c')
-rw-r--r--kernel/cpu.c19
1 files changed, 13 insertions, 6 deletions
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 90a3d017b90c..5d220234b3ca 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -86,6 +86,16 @@ static struct {
#define cpuhp_lock_acquire() lock_map_acquire(&cpu_hotplug.dep_map)
#define cpuhp_lock_release() lock_map_release(&cpu_hotplug.dep_map)
+static void apply_puts_pending(int max)
+{
+ int delta;
+
+ if (atomic_read(&cpu_hotplug.puts_pending) >= max) {
+ delta = atomic_xchg(&cpu_hotplug.puts_pending, 0);
+ cpu_hotplug.refcount -= delta;
+ }
+}
+
void get_online_cpus(void)
{
might_sleep();
@@ -93,6 +103,7 @@ void get_online_cpus(void)
return;
cpuhp_lock_acquire_read();
mutex_lock(&cpu_hotplug.lock);
+ apply_puts_pending(65536);
cpu_hotplug.refcount++;
mutex_unlock(&cpu_hotplug.lock);
}
@@ -105,6 +116,7 @@ bool try_get_online_cpus(void)
if (!mutex_trylock(&cpu_hotplug.lock))
return false;
cpuhp_lock_acquire_tryread();
+ apply_puts_pending(65536);
cpu_hotplug.refcount++;
mutex_unlock(&cpu_hotplug.lock);
return true;
@@ -161,12 +173,7 @@ void cpu_hotplug_begin(void)
cpuhp_lock_acquire();
for (;;) {
mutex_lock(&cpu_hotplug.lock);
- if (atomic_read(&cpu_hotplug.puts_pending)) {
- int delta;
-
- delta = atomic_xchg(&cpu_hotplug.puts_pending, 0);
- cpu_hotplug.refcount -= delta;
- }
+ apply_puts_pending(1);
if (likely(!cpu_hotplug.refcount))
break;
__set_current_state(TASK_UNINTERRUPTIBLE);

Privacy Policy