7 files changed, 36 insertions, 22 deletions

diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
index 911d2641f14c..62d02e3c3ed6 100644
--- a/arch/x86/kvm/trace.h
+++ b/arch/x86/kvm/trace.h
@@ -710,16 +710,6 @@ TRACE_EVENT(kvm_skinit,
                   __entry->rip, __entry->slb)
 );
 
-#define __print_insn(insn, ilen) ({                              \
-        int i;                                                   \
-        const char *ret = p->buffer + p->len;                    \
-                                                                 \
-        for (i = 0; i < ilen; ++i)                               \
-                trace_seq_printf(p, " %02x", insn[i]);           \
-        trace_seq_printf(p, "%c", 0);                            \
-        ret;                                                     \
-        })
-
 #define KVM_EMUL_INSN_F_CR0_PE (1 << 0)
 #define KVM_EMUL_INSN_F_EFL_VM (1 << 1)
 #define KVM_EMUL_INSN_F_CS_D   (1 << 2)
@@ -786,7 +776,7 @@ TRACE_EVENT(kvm_emulate_insn,
 
         TP_printk("%x:%llx:%s (%s)%s",
                   __entry->csbase, __entry->rip,
-                  __print_insn(__entry->insn, __entry->len),
+                  __print_hex(__entry->insn, __entry->len),
                   __print_symbolic(__entry->flags,
                                    kvm_trace_symbol_emul_flags),
                   __entry->failed ? " failed" : ""
diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 1aff18346c71..af961d6f7ab1 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -65,7 +65,7 @@ struct trace_iterator {
         void                    *private;
         int                     cpu_file;
         struct mutex            mutex;
-        struct ring_buffer_iter *buffer_iter[NR_CPUS];
+        struct ring_buffer_iter **buffer_iter;
         unsigned long           iter_flags;
 
         /* trace_seq for __print_flags() and __print_symbolic() etc. */
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 769724944fc6..c6bc2faaf261 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -571,6 +571,7 @@ static inline void ftrace_test_probe_##call(void)			\
 
 #undef __print_flags
 #undef __print_symbolic
+#undef __print_hex
 #undef __get_dynamic_array
 #undef __get_str
 
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 1d0f6a8a0e5e..82a3e0c56b1d 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -3239,6 +3239,10 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
         if (cpu_buffer->commit_page == cpu_buffer->reader_page)
                 goto out;
 
+        /* Don't bother swapping if the ring buffer is empty */
+        if (rb_num_of_entries(cpu_buffer) == 0)
+                goto out;
+
         /*
          * Reset the reader page to size zero.
          */
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a7fa0702be1c..814ff306ae74 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -830,6 +830,8 @@ int register_tracer(struct tracer *type)
                 current_trace = saved_tracer;
                 if (ret) {
                         printk(KERN_CONT "FAILED!\n");
+                        /* Add the warning after printing 'FAILED' */
+                        WARN_ON(1);
                         goto out;
                 }
                 /* Only reset on passing, to avoid touching corrupted buffers */
@@ -1708,9 +1710,11 @@ EXPORT_SYMBOL_GPL(trace_vprintk);
 
 static void trace_iterator_increment(struct trace_iterator *iter)
 {
+        struct ring_buffer_iter *buf_iter = trace_buffer_iter(iter, iter->cpu);
+
         iter->idx++;
-        if (iter->buffer_iter[iter->cpu])
-                ring_buffer_read(iter->buffer_iter[iter->cpu], NULL);
+        if (buf_iter)
+                ring_buffer_read(buf_iter, NULL);
 }
 
 static struct trace_entry *
@@ -1718,7 +1722,7 @@ peek_next_entry(struct trace_iterator *iter, int cpu, u64 *ts,
                 unsigned long *lost_events)
 {
         struct ring_buffer_event *event;
-        struct ring_buffer_iter *buf_iter = iter->buffer_iter[cpu];
+        struct ring_buffer_iter *buf_iter = trace_buffer_iter(iter, cpu);
 
         if (buf_iter)
                 event = ring_buffer_iter_peek(buf_iter, ts);
@@ -1856,10 +1860,10 @@ void tracing_iter_reset(struct trace_iterator *iter, int cpu)
 
         tr->data[cpu]->skipped_entries = 0;
 
-        if (!iter->buffer_iter[cpu])
+        buf_iter = trace_buffer_iter(iter, cpu);
+        if (!buf_iter)
                 return;
 
-        buf_iter = iter->buffer_iter[cpu];
         ring_buffer_iter_reset(buf_iter);
 
         /*
@@ -2205,13 +2209,15 @@ static enum print_line_t print_bin_fmt(struct trace_iterator *iter)
 
 int trace_empty(struct trace_iterator *iter)
 {
+        struct ring_buffer_iter *buf_iter;
         int cpu;
 
         /* If we are looking at one CPU buffer, only check that one */
         if (iter->cpu_file != TRACE_PIPE_ALL_CPU) {
                 cpu = iter->cpu_file;
-                if (iter->buffer_iter[cpu]) {
-                        if (!ring_buffer_iter_empty(iter->buffer_iter[cpu]))
+                buf_iter = trace_buffer_iter(iter, cpu);
+                if (buf_iter) {
+                        if (!ring_buffer_iter_empty(buf_iter))
                                 return 0;
                 } else {
                         if (!ring_buffer_empty_cpu(iter->tr->buffer, cpu))
@@ -2221,8 +2227,9 @@ int trace_empty(struct trace_iterator *iter)
         }
 
         for_each_tracing_cpu(cpu) {
-                if (iter->buffer_iter[cpu]) {
-                        if (!ring_buffer_iter_empty(iter->buffer_iter[cpu]))
+                buf_iter = trace_buffer_iter(iter, cpu);
+                if (buf_iter) {
+                        if (!ring_buffer_iter_empty(buf_iter))
                                 return 0;
                 } else {
                         if (!ring_buffer_empty_cpu(iter->tr->buffer, cpu))
@@ -2381,6 +2388,8 @@ __tracing_open(struct inode *inode, struct file *file)
         if (!iter)
                 return ERR_PTR(-ENOMEM);
 
+        iter->buffer_iter = kzalloc(sizeof(*iter->buffer_iter) * num_possible_cpus(),
+                                    GFP_KERNEL);
         /*
          * We make a copy of the current tracer to avoid concurrent
          * changes on it while we are reading.
@@ -2441,6 +2450,7 @@ __tracing_open(struct inode *inode, struct file *file)
  fail:
         mutex_unlock(&trace_types_lock);
         kfree(iter->trace);
+        kfree(iter->buffer_iter);
         seq_release_private(inode, file);
         return ERR_PTR(-ENOMEM);
 }
@@ -2481,6 +2491,7 @@ static int tracing_release(struct inode *inode, struct file *file)
         mutex_destroy(&iter->mutex);
         free_cpumask_var(iter->started);
         kfree(iter->trace);
+        kfree(iter->buffer_iter);
         seq_release_private(inode, file);
         return 0;
 }
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 5aec220d2de0..55e1f7f0db12 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -317,6 +317,14 @@ struct tracer {
 
 #define TRACE_PIPE_ALL_CPU      -1
 
+static inline struct ring_buffer_iter *
+trace_buffer_iter(struct trace_iterator *iter, int cpu)
+{
+        if (iter->buffer_iter && iter->buffer_iter[cpu])
+                return iter->buffer_iter[cpu];
+        return NULL;
+}
+
 int tracer_init(struct tracer *t, struct trace_array *tr);
 int tracing_is_enabled(void);
 void trace_wake_up(void);
diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index a7d2a4c653d8..ce27c8ba8d31 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -538,7 +538,7 @@ get_return_for_leaf(struct trace_iterator *iter,
                 next = &data->ret;
         } else {
 
-                ring_iter = iter->buffer_iter[iter->cpu];
+                ring_iter = trace_buffer_iter(iter, iter->cpu);
 
                 /* First peek to compare current entry and the next one */
                 if (ring_iter)