Commit 49516342 authored Feb 11, 2014 by Juri Lelli Committed by Thomas Gleixner Feb 21, 2014

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>

parent e9e7cb38

kernel/sched/core.c

+6 −4

Original line number	Diff line number	Diff line
		@@ -7422,6 +7422,7 @@ static int sched_dl_global_constraints(void)
		u64 period = global_rt_period();
		u64 new_bw = to_ratio(period, runtime);
		int cpu, ret = 0;
		unsigned long flags;

		/*
		* Here we want to check the bandwidth not being set to some
		@@ -7435,10 +7436,10 @@ static int sched_dl_global_constraints(void)
		for_each_possible_cpu(cpu) {
		struct dl_bw *dl_b = dl_bw_of(cpu);

		raw_spin_lock(&dl_b->lock);
		raw_spin_lock_irqsave(&dl_b->lock, flags);
		if (new_bw < dl_b->total_bw)
		ret = -EBUSY;
		raw_spin_unlock(&dl_b->lock);
		raw_spin_unlock_irqrestore(&dl_b->lock, flags);

		if (ret)
		break;
		@@ -7451,6 +7452,7 @@ static void sched_dl_do_global(void)
		{
		u64 new_bw = -1;
		int cpu;
		unsigned long flags;

		def_dl_bandwidth.dl_period = global_rt_period();
		def_dl_bandwidth.dl_runtime = global_rt_runtime();
		@@ -7464,9 +7466,9 @@ static void sched_dl_do_global(void)
		for_each_possible_cpu(cpu) {
		struct dl_bw *dl_b = dl_bw_of(cpu);

		raw_spin_lock(&dl_b->lock);
		raw_spin_lock_irqsave(&dl_b->lock, flags);
		dl_b->bw = new_bw;
		raw_spin_unlock(&dl_b->lock);
		raw_spin_unlock_irqrestore(&dl_b->lock, flags);
		}
		}

Admin message