sched/deadline: Fix bad accounting of nr_running

Rostedt writes:

My test suite was locking up hard when enabling mmiotracer. This was due
to the mmiotracer placing all but one CPU offline. I found this out
when I was able to reproduce the bug with just my stress-cpu-hotplug
test. This bug baffled me because it would not always trigger, and
would only trigger on the first run after boot up. The
stress-cpu-hotplug test would crash hard the first run, or never crash
at all. But a new reboot may cause it to crash on the first run again.

I spent all week bisecting this, as I couldn't find a consistent
reproducer. I finally narrowed it down to the sched deadline patches,
and even more peculiar, to the commit that added the sched
deadline boot up self test to the latency tracer. Then it dawned on me
to what the bug was.

All it took was to run a task under sched deadline to screw up the CPU
hot plugging. This explained why it would lock up only on the first run
of the stress-cpu-hotplug test. The bug happened when the boot up self
test of the schedule latency tracer would test a deadline task. The
deadline task would corrupt something that would cause CPU hotplug to
fail. If it didn't corrupt it, the stress test would always work
(there's no other sched deadline tasks that would run to cause
problems). If it did corrupt on boot up, the first test would lockup
hard.

I proved this theory by running my deadline test program on another box,
and then run the stress-cpu-hotplug test, and it would now consistently
lock up. I could run stress-cpu-hotplug over and over with no problem,
but once I ran the deadline test, the next run of the
stress-cpu-hotplug would lock hard.

After adding lots of tracing to the code, I found the cause. The
function tracer showed that migrate_tasks() was stuck in an infinite
loop, where rq->nr_running never equaled 1 to break out of it. When I
added a trace_printk() to see what that number was, it was 335 and
never decrementing!

Looking at the deadline code I found:

static void __dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags) {
	dequeue_dl_entity(&p->dl);
	dequeue_pushable_dl_task(rq, p);
}

static void dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags) {
	update_curr_dl(rq);
	__dequeue_task_dl(rq, p, flags);

	dec_nr_running(rq);
}

And this:

	if (dl_runtime_exceeded(rq, dl_se)) {
		__dequeue_task_dl(rq, curr, 0);
		if (likely(start_dl_timer(dl_se, curr->dl.dl_boosted)))
			dl_se->dl_throttled = 1;
		else
			enqueue_task_dl(rq, curr, ENQUEUE_REPLENISH);

		if (!is_leftmost(curr, &rq->dl))
			resched_task(curr);
	}

Notice how we call __dequeue_task_dl() and in the else case we
call enqueue_task_dl()? Also notice that dequeue_task_dl() has
underscores where enqueue_task_dl() does not. The enqueue_task_dl()
calls inc_nr_running(rq), but __dequeue_task_dl() does not. This is
where we get nr_running out of sync.

[snip]

Another point where nr_running can get out of sync is when the dl_timer
fires:

	dl_se->dl_throttled = 0;
	if (p->on_rq) {
		enqueue_task_dl(rq, p, ENQUEUE_REPLENISH);
		if (task_has_dl_policy(rq->curr))
			check_preempt_curr_dl(rq, p, 0);
		else
			resched_task(rq->curr);

This patch does two things:

 - correctly accounts for throttled tasks (that are now considered
   !running);

 - fixes the bug, updating nr_running from {inc,dec}_dl_tasks(),
   since we risk to update it twice in some situations (e.g., a
   task is dequeued while it has exceeded its budget).

Cc: mingo@redhat.com
Cc: torvalds@linux-foundation.org
Cc: akpm@linux-foundation.org
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Tested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Juri Lelli <juri.lelli@gmail.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1392884379-13744-1-git-send-email-juri.lelli@gmail.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Luis Cruz <ljc2491@gmail.com>
sched/deadline: Fix overflow to handle period==0 and deadline!=0

While debugging the crash with the bad nr_running accounting, I hit
another bug where, after running my sched deadline test, I was getting
failures to take a CPU offline. It was giving me a -EBUSY error.

Adding a bunch of trace_printk()s around, I found that the cpu
notifier that called sched_cpu_inactive() was returning a failure. The
overflow value was coming up negative?

Talking this over with Juri, the problem is that the total_bw update was
suppose to be made by dl_overflow() which, during my tests, seemed to
not be called. Adding more trace_printk()s, it wasn't that it wasn't
called, but it exited out right away with the check of new_bw being
equal to p->dl.dl_bw. The new_bw calculates the ratio between period and
runtime. The bug is that if you set a deadline, you do not need to set
a period if you plan on the period being equal to the deadline. That
is, if period is zero and deadline is not, then the system call should
set the period to be equal to the deadline. This is done elsewhere in
the code.

The fix is easy, check if period is set, and if it is not, then use the
deadline.

Cc: Juri Lelli <juri.lelli@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140219135335.7e74abd4@gandalf.local.home
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Luis Cruz <ljc2491@gmail.com>
sched/core: Fix sched_rt_global_validate

Don't compare sysctl_sched_rt_runtime against sysctl_sched_rt_period if
the former is equal to RUNTIME_INF, otherwise disabling -rt bandwidth
management (with CONFIG_RT_GROUP_SCHED=n) fails.

Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Juri Lelli <juri.lelli@gmail.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1392107067-19907-2-git-send-email-juri.lelli@gmail.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Luis Cruz <ljc2491@gmail.com>
sched/core: Make dl_b->lock IRQ safe

Fix this lockdep warning:

[   44.804600] =========================================================
[   44.805746] [ INFO: possible irq lock inversion dependency detected ]
[   44.805746] 3.14.0-rc2-test+ #14 Not tainted
[   44.805746] ---------------------------------------------------------
[   44.805746] bash/3674 just changed the state of lock:
[   44.805746]  (&dl_b->lock){+.....}, at: [<ffffffff8106ad15>] sched_rt_handler+0x132/0x248
[   44.805746] but this lock was taken by another, HARDIRQ-safe lock in the past:
[   44.805746]  (&rq->lock){-.-.-.}

and interrupts could create inverse lock ordering between them.

[   44.805746]
[   44.805746] other info that might help us debug this:
[   44.805746]  Possible interrupt unsafe locking scenario:
[   44.805746]
[   44.805746]        CPU0                    CPU1
[   44.805746]        ----                    ----
[   44.805746]   lock(&dl_b->lock);
[   44.805746]                                local_irq_disable();
[   44.805746]                                lock(&rq->lock);
[   44.805746]                                lock(&dl_b->lock);
[   44.805746]   <Interrupt>
[   44.805746]     lock(&rq->lock);

by making dl_b->lock acquiring always IRQ safe.

Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Juri Lelli <juri.lelli@gmail.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1392107067-19907-3-git-send-email-juri.lelli@gmail.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Luis Cruz <ljc2491@gmail.com>
sched: Fix information leak in sys_sched_getattr()

We're copying the on-stack structure to userspace, but forgot to give
the right number of bytes to copy. This allows the calling process to
obtain up to PAGE_SIZE bytes from the stack (and possibly adjacent
kernel memory).

This fix copies only as much as we actually have on the stack
(attr->size defaults to the size of the struct) and leaves the rest of
the userspace-provided buffer untouched.

Found using kmemcheck + trinity.

Fixes: d50dde5a10f30 ("sched: Add new scheduler syscalls to support an extended scheduling parameters ABI")
Cc: Dario Faggioli <raistlin@linux.it>
Cc: Juri Lelli <juri.lelli@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1392585857-10725-1-git-send-email-vegard.nossum@oracle.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Luis Cruz <ljc2491@gmail.com>
sched: Add 'flags' argument to sched_{set,get}attr() syscalls

Because of a recent syscall design debate; its deemed appropriate for
each syscall to have a flags argument for future extension; without
immediately requiring new syscalls.

Cc: juri.lelli@gmail.com
Cc: Ingo Molnar <mingo@redhat.com>
Suggested-by: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140214161929.GL27965@twins.programming.kicks-ass.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Luis Cruz <ljc2491@gmail.com>
sched/deadline: Test for CPU's presence explicitly

A hot-removed CPU may have ID that is numerically larger than the number of
existing CPUs in the system (e.g. we can unplug CPU 4 from a system that
has CPUs 0, 1 and 4).

Thus the WARN_ONs should check whether the CPU in question is currently
present, not whether its ID value is less than num_present_cpus().

Cc: Ingo Molnar <mingo@kernel.org>
Cc: Juri Lelli <juri.lelli@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1392646353-1874-1-git-send-email-boris.ostrovsky@oracle.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Luis Cruz <ljc2491@gmail.com>
sched/deadline: Remove useless dl_nr_total

In deadline class we do not have group scheduling like in RT.

dl_nr_total is the same as dl_nr_running. So, one of them should
be removed.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juri Lelli <juri.lelli@gmail.com>
Signed-off-by: Kirill Tkhai <tkhai@yandex.ru>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/368631392675853@web20h.yandex.ru
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

Conflicts:

	kernel/sched/deadline.c

Signed-off-by: Luis Cruz <ljc2491@gmail.com>