pstore/ftrace: Convert to its own enable/disable debugfs knob

With this patch we no longer reuse function tracer infrastructure, now
we register our own tracer back-end via a debugfs knob.

It's a bit more code, but that is the only downside. On the bright side we
have:

- Ability to make persistent_ram module removable (when needed, we can
  move ftrace_ops struct into a module). Note that persistent_ram is still
  not removable for other reasons, but with this patch it's just one
  thing less to worry about;

- Pstore part is more isolated from the generic function tracer. We tried
  it already by registering our own tracer in available_tracers, but that
  way we're loosing ability to see the traces while we record them to
  pstore. This solution is somewhere in the middle: we only register
  "internal ftracer" back-end, but not the "front-end";

- When there is only pstore tracing enabled, the kernel will only write
  to the pstore buffer, omitting function tracer buffer (which, of course,
  still can be enabled via 'echo function > current_tracer').

Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>

1 files changed, 1 insertions, 14 deletions

diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
index a426f410c06..0ad83e3929d 100644
--- a/kernel/trace/trace_functions.c
+++ b/kernel/trace/trace_functions.c
@@ -13,7 +13,6 @@
 #include <linux/debugfs.h>
 #include <linux/uaccess.h>
 #include <linux/ftrace.h>
-#include <linux/pstore.h>
 #include <linux/fs.h>
 
 #include "trace.h"
@@ -75,10 +74,9 @@ function_trace_call_preempt_only(unsigned long ip, unsigned long parent_ip)
         preempt_enable_notrace();
 }
 
-/* Our two options */
+/* Our option */
 enum {
         TRACE_FUNC_OPT_STACK    = 0x1,
-        TRACE_FUNC_OPT_PSTORE   = 0x2,
 };
 
 static struct tracer_flags func_flags;
@@ -106,12 +104,6 @@ function_trace_call(unsigned long ip, unsigned long parent_ip)
         disabled = atomic_inc_return(&data->disabled);
 
         if (likely(disabled == 1)) {
-                /*
-                 * So far tracing doesn't support multiple buffers, so
-                 * we make an explicit call for now.
-                 */
-                if (unlikely(func_flags.val & TRACE_FUNC_OPT_PSTORE))
-                        pstore_ftrace_call(ip, parent_ip);
                 pc = preempt_count();
                 trace_function(tr, ip, parent_ip, flags, pc);
         }
@@ -177,9 +169,6 @@ static struct tracer_opt func_opts[] = {
 #ifdef CONFIG_STACKTRACE
         { TRACER_OPT(func_stack_trace, TRACE_FUNC_OPT_STACK) },
 #endif
-#ifdef CONFIG_PSTORE_FTRACE
-        { TRACER_OPT(func_pstore, TRACE_FUNC_OPT_PSTORE) },
-#endif
         { } /* Always set a last empty entry */
 };
 
@@ -232,8 +221,6 @@ static int func_set_flag(u32 old_flags, u32 bit, int set)
                 }
 
                 break;
-        case TRACE_FUNC_OPT_PSTORE:
-                break;
         default:
                 return -EINVAL;
         }