3 files changed, 87 insertions, 19 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index d9c16123f6e2..e5df02c69b1d 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1248,6 +1248,15 @@ ftrace(struct trace_array *tr, struct trace_array_cpu *data,
 }
 
 #ifdef CONFIG_STACKTRACE
+
+#define FTRACE_STACK_MAX_ENTRIES (PAGE_SIZE / sizeof(unsigned long))
+struct ftrace_stack {
+        unsigned long           calls[FTRACE_STACK_MAX_ENTRIES];
+};
+
+static DEFINE_PER_CPU(struct ftrace_stack, ftrace_stack);
+static DEFINE_PER_CPU(int, ftrace_stack_reserve);
+
 static void __ftrace_trace_stack(struct ring_buffer *buffer,
                                  unsigned long flags,
                                  int skip, int pc, struct pt_regs *regs)
@@ -1256,25 +1265,77 @@ static void __ftrace_trace_stack(struct ring_buffer *buffer,
         struct ring_buffer_event *event;
         struct stack_entry *entry;
         struct stack_trace trace;
+        int use_stack;
+        int size = FTRACE_STACK_ENTRIES;
+
+        trace.nr_entries        = 0;
+        trace.skip              = skip;
+
+        /*
+         * Since events can happen in NMIs there's no safe way to
+         * use the per cpu ftrace_stacks. We reserve it and if an interrupt
+         * or NMI comes in, it will just have to use the default
+         * FTRACE_STACK_SIZE.
+         */
+        preempt_disable_notrace();
+
+        use_stack = ++__get_cpu_var(ftrace_stack_reserve);
+        /*
+         * We don't need any atomic variables, just a barrier.
+         * If an interrupt comes in, we don't care, because it would
+         * have exited and put the counter back to what we want.
+         * We just need a barrier to keep gcc from moving things
+         * around.
+         */
+        barrier();
+        if (use_stack == 1) {
+                trace.entries           = &__get_cpu_var(ftrace_stack).calls[0];
+                trace.max_entries       = FTRACE_STACK_MAX_ENTRIES;
+
+                if (regs)
+                        save_stack_trace_regs(regs, &trace);
+                else
+                        save_stack_trace(&trace);
+
+                if (trace.nr_entries > size)
+                        size = trace.nr_entries;
+        } else
+                /* From now on, use_stack is a boolean */
+                use_stack = 0;
+
+        size *= sizeof(unsigned long);
 
         event = trace_buffer_lock_reserve(buffer, TRACE_STACK,
-                                          sizeof(*entry), flags, pc);
+                                          sizeof(*entry) + size, flags, pc);
         if (!event)
-                return;
-        entry   = ring_buffer_event_data(event);
-        memset(&entry->caller, 0, sizeof(entry->caller));
+                goto out;
+        entry = ring_buffer_event_data(event);
 
-        trace.nr_entries        = 0;
-        trace.max_entries       = FTRACE_STACK_ENTRIES;
-        trace.skip              = skip;
-        trace.entries           = entry->caller;
+        memset(&entry->caller, 0, size);
+
+        if (use_stack)
+                memcpy(&entry->caller, trace.entries,
+                       trace.nr_entries * sizeof(unsigned long));
+        else {
+                trace.max_entries       = FTRACE_STACK_ENTRIES;
+                trace.entries           = entry->caller;
+                if (regs)
+                        save_stack_trace_regs(regs, &trace);
+                else
+                        save_stack_trace(&trace);
+        }
+
+        entry->size = trace.nr_entries;
 
-        if (regs)
-                save_stack_trace_regs(regs, &trace);
-        else
-                save_stack_trace(&trace);
         if (!filter_check_discard(call, entry, buffer, event))
                 ring_buffer_unlock_commit(buffer, event);
+
+ out:
+        /* Again, don't let gcc optimize things here */
+        barrier();
+        __get_cpu_var(ftrace_stack_reserve)--;
+        preempt_enable_notrace();
+
 }
 
 void ftrace_trace_stack_regs(struct ring_buffer *buffer, unsigned long flags,
@@ -1562,7 +1623,12 @@ peek_next_entry(struct trace_iterator *iter, int cpu, u64 *ts,
 
         ftrace_enable_cpu();
 
-        return event ? ring_buffer_event_data(event) : NULL;
+        if (event) {
+                iter->ent_size = ring_buffer_event_length(event);
+                return ring_buffer_event_data(event);
+        }
+        iter->ent_size = 0;
+        return NULL;
 }
 
 static struct trace_entry *
diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
index e32744c84d94..93365907f219 100644
--- a/kernel/trace/trace_entries.h
+++ b/kernel/trace/trace_entries.h
@@ -161,7 +161,8 @@ FTRACE_ENTRY(kernel_stack, stack_entry,
         TRACE_STACK,
 
         F_STRUCT(
-                __array(        unsigned long,  caller, FTRACE_STACK_ENTRIES    )
+                __field(        int,            size    )
+                __dynamic_array(unsigned long,  caller  )
         ),
 
         F_printk("\t=> (%08lx)\n\t=> (%08lx)\n\t=> (%08lx)\n\t=> (%08lx)\n"
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index e37de492a9e1..51999309a6cf 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -1107,19 +1107,20 @@ static enum print_line_t trace_stack_print(struct trace_iterator *iter,
 {
         struct stack_entry *field;
         struct trace_seq *s = &iter->seq;
-        int i;
+        unsigned long *p;
+        unsigned long *end;
 
         trace_assign_type(field, iter->ent);
+        end = (unsigned long *)((long)iter->ent + iter->ent_size);
 
         if (!trace_seq_puts(s, "<stack trace>\n"))
                 goto partial;
-        for (i = 0; i < FTRACE_STACK_ENTRIES; i++) {
-                if (!field->caller[i] || (field->caller[i] == ULONG_MAX))
-                        break;
+
+        for (p = field->caller; p && *p != ULONG_MAX && p < end; p++) {
                 if (!trace_seq_puts(s, " => "))
                         goto partial;
 
-                if (!seq_print_ip_sym(s, field->caller[i], flags))
+                if (!seq_print_ip_sym(s, *p, flags))
                         goto partial;
                 if (!trace_seq_puts(s, "\n"))
                         goto partial;