sched/membarrier: reduce the ability to hammer on sys_membarrier

On some systems, sys_membarrier can be very expensive, causing overall
slowdowns for everything.  So put a lock on the path in order to
serialize the accesses to prevent the ability for this to be called at
too high of a frequency and saturate the machine.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-and-tested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Fixes: 22e4ebb97582 ("membarrier: Provide expedited private command")
Fixes: c5f58bd58f43 ("membarrier: Provide GLOBAL_EXPEDITED command")
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
index 2ad881d07752c15f60a4c14bee21051117d5aeb2..4e715b9b278e7fd7fbea70110f5a829635a4bc01 100644 (file)
--- a/kernel/sched/membarrier.c
+++ b/kernel/sched/membarrier.c
@@ -162,6 +162,9 @@
        | MEMBARRIER_PRIVATE_EXPEDITED_RSEQ_BITMASK                     \
        | MEMBARRIER_CMD_GET_REGISTRATIONS)
 
+static DEFINE_MUTEX(membarrier_ipi_mutex);
+#define SERIALIZE_IPI() guard(mutex)(&membarrier_ipi_mutex)
+
 static void ipi_mb(void *info)
 {
        smp_mb();       /* IPIs should be serializing but paranoid. */
@@ -259,6 +262,7 @@ static int membarrier_global_expedited(void)
        if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
                return -ENOMEM;
 
+       SERIALIZE_IPI();
        cpus_read_lock();
        rcu_read_lock();
        for_each_online_cpu(cpu) {
@@ -347,6 +351,7 @@ static int membarrier_private_expedited(int flags, int cpu_id)
        if (cpu_id < 0 && !zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
                return -ENOMEM;
 
+       SERIALIZE_IPI();
        cpus_read_lock();
 
        if (cpu_id >= 0) {
@@ -460,6 +465,7 @@ static int sync_runqueues_membarrier_state(struct mm_struct *mm)
         * between threads which are users of @mm has its membarrier state
         * updated.
         */
+       SERIALIZE_IPI();
        cpus_read_lock();
        rcu_read_lock();
        for_each_online_cpu(cpu) {