tracing: Add alloc_snapshot kernel command line parameter

If debugging the kernel, and the developer wants to use
tracing_snapshot() in places where tracing_snapshot_alloc() may
be difficult (or more likely, the developer is lazy and doesn't
want to bother with tracing_snapshot_alloc() at all), then adding

  alloc_snapshot

to the kernel command line parameter will tell ftrace to allocate
the snapshot buffer (if configured) when it allocates the main
tracing buffer.

I also noticed that ring_buffer_expanded and tracing_selftest_disabled
had inconsistent use of boolean "true" and "false" with "0" and "1".
I cleaned that up too.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 6c723811c0a09f3ad5b2b18fa32ef12aa55cd82a..0edc409f9eded380ec0d15384505ae6d325dfb73 100644 (file)
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -320,6 +320,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                        on: enable for both 32- and 64-bit processes
                        off: disable for both 32- and 64-bit processes
 
+       alloc_snapshot  [FTRACE]
+                       Allocate the ftrace snapshot buffer on boot up when the
+                       main buffer is allocated. This is handy if debugging
+                       and you need to use tracing_snapshot() on boot up, and
+                       do not want to use tracing_snapshot_alloc() as it needs
+                       to be done where GFP_KERNEL allocations are allowed.
+
        amd_iommu=      [HW,X86-64]
                        Pass parameters to the AMD IOMMU driver in the system.
                        Possible values are:

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 57b4220d96a9d14244441b192b1735b8735b7001..4021a5e6641285fd846948604577bb687e21a795 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -47,7 +47,7 @@
  * On boot up, the ring buffer is set to the minimum size, so that
  * we do not waste memory on systems that are not using tracing.
  */
-int ring_buffer_expanded;
+bool ring_buffer_expanded;
 
 /*
  * We need to change this state when a selftest is running.
@@ -121,12 +121,14 @@ static int tracing_set_tracer(const char *buf);
 static char bootup_tracer_buf[MAX_TRACER_SIZE] __initdata;
 static char *default_bootup_tracer;
 
+static bool allocate_snapshot;
+
 static int __init set_cmdline_ftrace(char *str)
 {
        strncpy(bootup_tracer_buf, str, MAX_TRACER_SIZE);
        default_bootup_tracer = bootup_tracer_buf;
        /* We are using ftrace early, expand it */
-       ring_buffer_expanded = 1;
+       ring_buffer_expanded = true;
        return 1;
 }
 __setup("ftrace=", set_cmdline_ftrace);
@@ -147,6 +149,15 @@ static int __init set_ftrace_dump_on_oops(char *str)
 }
 __setup("ftrace_dump_on_oops", set_ftrace_dump_on_oops);
 
+static int __init alloc_snapshot(char *str)
+{
+       allocate_snapshot = true;
+       /* We also need the main ring buffer expanded */
+       ring_buffer_expanded = true;
+       return 1;
+}
+__setup("alloc_snapshot", alloc_snapshot);
+
 
 static char trace_boot_options_buf[MAX_TRACER_SIZE] __initdata;
 static char *trace_boot_options __initdata;
@@ -951,7 +962,7 @@ int register_tracer(struct tracer *type)
        tracing_set_tracer(type->name);
        default_bootup_tracer = NULL;
        /* disable other selftests, since this will break it. */
-       tracing_selftest_disabled = 1;
+       tracing_selftest_disabled = true;
 #ifdef CONFIG_FTRACE_STARTUP_TEST
        printk(KERN_INFO "Disabling FTRACE selftests due to running tracer '%s'\n",
               type->name);
@@ -3318,7 +3329,7 @@ static int __tracing_resize_ring_buffer(struct trace_array *tr,
         * we use the size that was given, and we can forget about
         * expanding it later.
         */
-       ring_buffer_expanded = 1;
+       ring_buffer_expanded = true;
 
        /* May be called before buffers are initialized */
        if (!tr->trace_buffer.buffer)
@@ -5396,53 +5407,57 @@ static void init_trace_buffers(struct trace_array *tr, struct trace_buffer *buf)
        }
 }
 
-static int allocate_trace_buffers(struct trace_array *tr, int size)
+static int
+allocate_trace_buffer(struct trace_array *tr, struct trace_buffer *buf, int size)
 {
        enum ring_buffer_flags rb_flags;
 
        rb_flags = trace_flags & TRACE_ITER_OVERWRITE ? RB_FL_OVERWRITE : 0;
 
-       tr->trace_buffer.buffer = ring_buffer_alloc(size, rb_flags);
-       if (!tr->trace_buffer.buffer)
-               goto out_free;
+       buf->buffer = ring_buffer_alloc(size, rb_flags);
+       if (!buf->buffer)
+               return -ENOMEM;
 
-       tr->trace_buffer.data = alloc_percpu(struct trace_array_cpu);
-       if (!tr->trace_buffer.data)
-               goto out_free;
+       buf->data = alloc_percpu(struct trace_array_cpu);
+       if (!buf->data) {
+               ring_buffer_free(buf->buffer);
+               return -ENOMEM;
+       }
 
-       init_trace_buffers(tr, &tr->trace_buffer);
+       init_trace_buffers(tr, buf);
 
        /* Allocate the first page for all buffers */
        set_buffer_entries(&tr->trace_buffer,
                           ring_buffer_size(tr->trace_buffer.buffer, 0));
 
-#ifdef CONFIG_TRACER_MAX_TRACE
-
-       tr->max_buffer.buffer = ring_buffer_alloc(1, rb_flags);
-       if (!tr->max_buffer.buffer)
-               goto out_free;
-
-       tr->max_buffer.data = alloc_percpu(struct trace_array_cpu);
-       if (!tr->max_buffer.data)
-               goto out_free;
+       return 0;
+}
 
-       init_trace_buffers(tr, &tr->max_buffer);
+static int allocate_trace_buffers(struct trace_array *tr, int size)
+{
+       int ret;
 
-       set_buffer_entries(&tr->max_buffer, 1);
-#endif
-       return 0;
+       ret = allocate_trace_buffer(tr, &tr->trace_buffer, size);
+       if (ret)
+               return ret;
 
- out_free:
-       if (tr->trace_buffer.buffer)
+#ifdef CONFIG_TRACER_MAX_TRACE
+       ret = allocate_trace_buffer(tr, &tr->max_buffer,
+                                   allocate_snapshot ? size : 1);
+       if (WARN_ON(ret)) {
                ring_buffer_free(tr->trace_buffer.buffer);
-       free_percpu(tr->trace_buffer.data);
+               free_percpu(tr->trace_buffer.data);
+               return -ENOMEM;
+       }
+       tr->allocated_snapshot = allocate_snapshot;
 
-#ifdef CONFIG_TRACER_MAX_TRACE
-       if (tr->max_buffer.buffer)
-               ring_buffer_free(tr->max_buffer.buffer);
-       free_percpu(tr->max_buffer.data);
+       /*
+        * Only the top level trace array gets its snapshot allocated
+        * from the kernel command line.
+        */
+       allocate_snapshot = false;
 #endif
-       return -ENOMEM;
+       return 0;
 }
 
 static int new_instance_create(const char *name)

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index f4931821a96699ad89ccf7f51fc4e4762bdcf303..26bc718340418b276dcf328ac6e78fde5f2ffa06 100644 (file)
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -660,7 +660,7 @@ extern int DYN_FTRACE_TEST_NAME(void);
 #define DYN_FTRACE_TEST_NAME2 trace_selftest_dynamic_test_func2
 extern int DYN_FTRACE_TEST_NAME2(void);
 
-extern int ring_buffer_expanded;
+extern bool ring_buffer_expanded;
 extern bool tracing_selftest_disabled;
 DECLARE_PER_CPU(int, ftrace_cpu_disabled);
 

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index a376ab5eec5cbcef90c210cb584d0bb46b97d4c2..38b54c5edeb9c0d2643af73432c1cff3c4e92797 100644 (file)
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1844,8 +1844,8 @@ static char bootup_event_buf[COMMAND_LINE_SIZE] __initdata;
 static __init int setup_trace_event(char *str)
 {
        strlcpy(bootup_event_buf, str, COMMAND_LINE_SIZE);
-       ring_buffer_expanded = 1;
-       tracing_selftest_disabled = 1;
+       ring_buffer_expanded = true;
+       tracing_selftest_disabled = true;
 
        return 1;
 }