1 files changed, 30 insertions, 14 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 3c13e46d7d24..d2a658349ca1 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -709,10 +709,14 @@ update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
                 return;
 
         WARN_ON_ONCE(!irqs_disabled());
-        if (!current_trace->use_max_tr) {
-                WARN_ON_ONCE(1);
+
+        /* If we disabled the tracer, stop now */
+        if (current_trace == &nop_trace)
                 return;
-        }
+
+        if (WARN_ON_ONCE(!current_trace->use_max_tr))
+                return;
+
         arch_spin_lock(&ftrace_max_lock);
 
         tr->buffer = max_tr.buffer;
@@ -922,6 +926,9 @@ void tracing_reset(struct trace_array *tr, int cpu)
 {
         struct ring_buffer *buffer = tr->buffer;
 
+        if (!buffer)
+                return;
+
         ring_buffer_record_disable(buffer);
 
         /* Make sure all commits have finished */
@@ -936,6 +943,9 @@ void tracing_reset_online_cpus(struct trace_array *tr)
         struct ring_buffer *buffer = tr->buffer;
         int cpu;
 
+        if (!buffer)
+                return;
+
         ring_buffer_record_disable(buffer);
 
         /* Make sure all commits have finished */
@@ -1167,7 +1177,6 @@ tracing_generic_entry_update(struct trace_entry *entry, unsigned long flags,
 
         entry->preempt_count            = pc & 0xff;
         entry->pid                      = (tsk) ? tsk->pid : 0;
-        entry->padding                  = 0;
         entry->flags =
 #ifdef CONFIG_TRACE_IRQFLAGS_SUPPORT
                 (irqs_disabled_flags(flags) ? TRACE_FLAG_IRQS_OFF : 0) |
@@ -1517,7 +1526,6 @@ static struct trace_buffer_struct *trace_percpu_nmi_buffer;
 static char *get_trace_buf(void)
 {
         struct trace_buffer_struct *percpu_buffer;
-        struct trace_buffer_struct *buffer;
 
         /*
          * If we have allocated per cpu buffers, then we do not
@@ -1535,9 +1543,7 @@ static char *get_trace_buf(void)
         if (!percpu_buffer)
                 return NULL;
 
-        buffer = per_cpu_ptr(percpu_buffer, smp_processor_id());
-
-        return buffer->buffer;
+        return this_cpu_ptr(&percpu_buffer->buffer[0]);
 }
 
 static int alloc_percpu_trace_buffer(void)
@@ -3183,6 +3189,7 @@ static int tracing_set_tracer(const char *buf)
         static struct trace_option_dentry *topts;
         struct trace_array *tr = &global_trace;
         struct tracer *t;
+        bool had_max_tr;
         int ret = 0;
 
         mutex_lock(&trace_types_lock);
@@ -3209,7 +3216,19 @@ static int tracing_set_tracer(const char *buf)
         trace_branch_disable();
         if (current_trace && current_trace->reset)
                 current_trace->reset(tr);
-        if (current_trace && current_trace->use_max_tr) {
+
+        had_max_tr = current_trace && current_trace->use_max_tr;
+        current_trace = &nop_trace;
+
+        if (had_max_tr && !t->use_max_tr) {
+                /*
+                 * We need to make sure that the update_max_tr sees that
+                 * current_trace changed to nop_trace to keep it from
+                 * swapping the buffers after we resize it.
+                 * The update_max_tr is called from interrupts disabled
+                 * so a synchronized_sched() is sufficient.
+                 */
+                synchronize_sched();
                 /*
                  * We don't free the ring buffer. instead, resize it because
                  * The max_tr ring buffer has some state (e.g. ring->clock) and
@@ -3220,10 +3239,8 @@ static int tracing_set_tracer(const char *buf)
         }
         destroy_trace_option_files(topts);
 
-        current_trace = &nop_trace;
-
         topts = create_trace_option_files(t);
-        if (t->use_max_tr) {
+        if (t->use_max_tr && !had_max_tr) {
                 /* we need to make per cpu buffer sizes equivalent */
                 ret = resize_buffer_duplicate_size(&max_tr, &global_trace,
                                                    RING_BUFFER_ALL_CPUS);
@@ -4037,8 +4054,7 @@ static ssize_t tracing_clock_write(struct file *filp, const char __user *ubuf,
          * Reset the buffer so that it doesn't have incomparable timestamps.
          */
         tracing_reset_online_cpus(&global_trace);
-        if (max_tr.buffer)
-                tracing_reset_online_cpus(&max_tr);
+        tracing_reset_online_cpus(&max_tr);
 
         mutex_unlock(&trace_types_lock);