Commit c172e0a3 authored by Mathieu Desnoyers's avatar Mathieu Desnoyers Committed by Ingo Molnar
Browse files

sched/membarrier: Return -ENOMEM to userspace on memory allocation failure 



Remove the IPI fallback code from membarrier to deal with very
infrequent cpumask memory allocation failure. Use GFP_KERNEL rather
than GFP_NOWAIT, and relax the blocking guarantees for the expedited
membarrier system call commands, allowing it to block if waiting for
memory to be made available.

In addition, now -ENOMEM can be returned to user-space if the cpumask
memory allocation fails.

Signed-off-by: default avatarMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Kirill Tkhai <tkhai@yandex.ru>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190919173705.2181-8-mathieu.desnoyers@efficios.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent c6d68c1c

kernel/sched/membarrier.c

+20 −43
Original line number Diff line number Diff line
@@ -66,7 +66,6 @@ void membarrier_exec_mmap(struct mm_struct *mm) 
static int membarrier_global_expedited(void)

{

	int cpu;

	bool fallback = false;

	cpumask_var_t tmpmask;



	if (num_online_cpus() == 1)
@@ -78,15 +77,8 @@ static int membarrier_global_expedited(void) 
	 */

	smp_mb();	/* system call entry is not a mb. */



	/*

	 * Expedited membarrier commands guarantee that they won't

	 * block, hence the GFP_NOWAIT allocation flag and fallback

	 * implementation.

	 */

	if (!zalloc_cpumask_var(&tmpmask, GFP_NOWAIT)) {

		/* Fallback for OOM. */

		fallback = true;

	}

	if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))

		return -ENOMEM;



	cpus_read_lock();

	rcu_read_lock();
@@ -117,18 +109,15 @@ static int membarrier_global_expedited(void) 
		if (p->flags & PF_KTHREAD)

			continue;



		if (!fallback)

		__cpumask_set_cpu(cpu, tmpmask);

		else

			smp_call_function_single(cpu, ipi_mb, NULL, 1);

	}

	rcu_read_unlock();

	if (!fallback) {



	preempt_disable();

	smp_call_function_many(tmpmask, ipi_mb, NULL, 1);

	preempt_enable();



	free_cpumask_var(tmpmask);

	}

	cpus_read_unlock();



	/*
@@ -143,7 +132,6 @@ static int membarrier_global_expedited(void) 
static int membarrier_private_expedited(int flags)

{

	int cpu;

	bool fallback = false;

	cpumask_var_t tmpmask;

	struct mm_struct *mm = current->mm;
@@ -168,15 +156,8 @@ static int membarrier_private_expedited(int flags) 
	 */

	smp_mb();	/* system call entry is not a mb. */



	/*

	 * Expedited membarrier commands guarantee that they won't

	 * block, hence the GFP_NOWAIT allocation flag and fallback

	 * implementation.

	 */

	if (!zalloc_cpumask_var(&tmpmask, GFP_NOWAIT)) {

		/* Fallback for OOM. */

		fallback = true;

	}

	if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))

		return -ENOMEM;



	cpus_read_lock();

	rcu_read_lock();
@@ -195,20 +176,16 @@ static int membarrier_private_expedited(int flags) 
			continue;

		rcu_read_lock();

		p = rcu_dereference(cpu_rq(cpu)->curr);

		if (p && p->mm == mm) {

			if (!fallback)

		if (p && p->mm == mm)

			__cpumask_set_cpu(cpu, tmpmask);

			else

				smp_call_function_single(cpu, ipi_mb, NULL, 1);

		}

	}

	rcu_read_unlock();

	if (!fallback) {



	preempt_disable();

	smp_call_function_many(tmpmask, ipi_mb, NULL, 1);

	preempt_enable();



	free_cpumask_var(tmpmask);

	}

	cpus_read_unlock();



	/*
@@ -264,7 +241,7 @@ static int sync_runqueues_membarrier_state(struct mm_struct *mm) 
		struct rq *rq = cpu_rq(cpu);

		struct task_struct *p;



		p = rcu_dereference(&rq->curr);

		p = rcu_dereference(rq->curr);

		if (p && p->mm == mm)

			__cpumask_set_cpu(cpu, tmpmask);

	}

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