From c172e0a3e8e65a4c6fffec5bc4d6de08d6f894f7 Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Thu, 19 Sep 2019 13:37:05 -0400 Subject: [PATCH] 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: Mathieu Desnoyers Signed-off-by: Peter Zijlstra (Intel) Cc: Chris Metcalf Cc: Christoph Lameter Cc: Eric W. Biederman Cc: Kirill Tkhai Cc: Linus Torvalds Cc: Mike Galbraith Cc: Oleg Nesterov Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Russell King - ARM Linux admin Cc: Thomas Gleixner Link: https://lkml.kernel.org/r/20190919173705.2181-8-mathieu.desnoyers@efficios.com Signed-off-by: Ingo Molnar --- kernel/sched/membarrier.c | 63 +++++++++++++-------------------------- 1 file changed, 20 insertions(+), 43 deletions(-) diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c index fced54ad0f3d..a39bed2c784f 100644 --- a/kernel/sched/membarrier.c +++ b/kernel/sched/membarrier.c @@ -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); + __cpumask_set_cpu(cpu, tmpmask); } rcu_read_unlock(); - if (!fallback) { - preempt_disable(); - smp_call_function_many(tmpmask, ipi_mb, NULL, 1); - preempt_enable(); - free_cpumask_var(tmpmask); - } + + 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) - __cpumask_set_cpu(cpu, tmpmask); - else - smp_call_function_single(cpu, ipi_mb, NULL, 1); - } + if (p && p->mm == mm) + __cpumask_set_cpu(cpu, tmpmask); } rcu_read_unlock(); - if (!fallback) { - preempt_disable(); - smp_call_function_many(tmpmask, ipi_mb, NULL, 1); - preempt_enable(); - free_cpumask_var(tmpmask); - } + + 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); }