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 <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter 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: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
index fced54ad0f3d406466cc239ae40b14be1426f9d0..a39bed2c784f42be244082e5d80320f72e9d8daf 100644 (file)
--- 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);
        }