On Thu, Sep 08, 2016 at 11:09:28AM -0700, Tim Chen wrote:

On Thu, Sep 08, 2016 at 09:59:55AM +0200, Peter Zijlstra wrote:

quoted

I think there's a race here, if two tasks were to write to the sysctl
they'd both change the value before getting stuck on the mutex in
enable_sched_itmt().

One way around that is doing something like:


	struct ctl_table t;
	int val = sysctl_sched_itmt_enabled;

	t = *table;
	t.data = &val;

	proc_dointvec_minmax(&t, ...);

	/* and update the sysctl_sched_itmt_enabled value inside the mutex */
	enable_sched_itmi(val);

Peter,

Since enable_sched_itmt is only used by sched_itmt_update_handler,
I've moved the mutex locking to sched_itmt_update_handler to eliminate
the race condition in the code path you mentioned.

That is indeed simpler. Thanks!