1 files changed, 50 insertions, 8 deletions

diff --git a/kernel/smp.c b/kernel/smp.c
index 96fc7c0edc59..782e2b93e465 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -135,7 +135,8 @@ void generic_smp_call_function_interrupt(void)
                          */
                         smp_wmb();
                         data->csd.flags &= ~CSD_FLAG_WAIT;
-                } else
+                }
+                if (data->csd.flags & CSD_FLAG_ALLOC)
                         call_rcu(&data->rcu_head, rcu_free_call_data);
         }
         rcu_read_unlock();
@@ -260,6 +261,42 @@ void __smp_call_function_single(int cpu, struct call_single_data *data)
         generic_exec_single(cpu, data);
 }
 
+/* Dummy function */
+static void quiesce_dummy(void *unused)
+{
+}
+
+/*
+ * Ensure stack based data used in call function mask is safe to free.
+ *
+ * This is needed by smp_call_function_mask when using on-stack data, because
+ * a single call function queue is shared by all CPUs, and any CPU may pick up
+ * the data item on the queue at any time before it is deleted. So we need to
+ * ensure that all CPUs have transitioned through a quiescent state after
+ * this call.
+ *
+ * This is a very slow function, implemented by sending synchronous IPIs to
+ * all possible CPUs. For this reason, we have to alloc data rather than use
+ * stack based data even in the case of synchronous calls. The stack based
+ * data is then just used for deadlock/oom fallback which will be very rare.
+ *
+ * If a faster scheme can be made, we could go back to preferring stack based
+ * data -- the data allocation/free is non-zero cost.
+ */
+static void smp_call_function_mask_quiesce_stack(cpumask_t mask)
+{
+        struct call_single_data data;
+        int cpu;
+
+        data.func = quiesce_dummy;
+        data.info = NULL;
+
+        for_each_cpu_mask(cpu, mask) {
+                data.flags = CSD_FLAG_WAIT;
+                generic_exec_single(cpu, &data);
+        }
+}
+
 /**
  * smp_call_function_mask(): Run a function on a set of other CPUs.
  * @mask: The set of cpus to run on.
@@ -285,6 +322,7 @@ int smp_call_function_mask(cpumask_t mask, void (*func)(void *), void *info,
         cpumask_t allbutself;
         unsigned long flags;
         int cpu, num_cpus;
+        int slowpath = 0;
 
         /* Can deadlock when called with interrupts disabled */
         WARN_ON(irqs_disabled());
@@ -306,15 +344,16 @@ int smp_call_function_mask(cpumask_t mask, void (*func)(void *), void *info,
                 return smp_call_function_single(cpu, func, info, wait);
         }
 
-        if (!wait) {
-                data = kmalloc(sizeof(*data), GFP_ATOMIC);
-                if (data)
-                        data->csd.flags = CSD_FLAG_ALLOC;
-        }
-        if (!data) {
+        data = kmalloc(sizeof(*data), GFP_ATOMIC);
+        if (data) {
+                data->csd.flags = CSD_FLAG_ALLOC;
+                if (wait)
+                        data->csd.flags |= CSD_FLAG_WAIT;
+        } else {
                 data = &d;
                 data->csd.flags = CSD_FLAG_WAIT;
                 wait = 1;
+                slowpath = 1;
         }
 
         spin_lock_init(&data->lock);
@@ -331,8 +370,11 @@ int smp_call_function_mask(cpumask_t mask, void (*func)(void *), void *info,
         arch_send_call_function_ipi(mask);
 
         /* optionally wait for the CPUs to complete */
-        if (wait)
+        if (wait) {
                 csd_flag_wait(&data->csd);
+                if (unlikely(slowpath))
+                        smp_call_function_mask_quiesce_stack(mask);
+        }
 
         return 0;
 }