Commit 62db99f4 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: default avatarPranith Kumar <bobby.prani@gmail.com>
parent 8fa7845d

kernel/cpu.c

+13 −6
Original line number Diff line number Diff line
@@ -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);

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