[PATCH] ftrace: fix ftraced and suspend to ram

[Rafael J . Wysocki]

Steven Rostedt observed:

> In latest 2.6.27(git) enabling dynamic ftrace makes resume from a suspend
> to ram reboot instead of resuming. Queued for 2.6.28 is a new method of
> recording mcount callers at compile time that does not have this issue.
>
> But the new method is still too "green" to be pulled into 27, so the old
> ftraced (daemon method) needs to be fixed for 27.
>
> The way dynamic ftrace works with the daemon method is this. On boot up
> the mcount function simply returns. When ftrace is initialized, it calls
> kstop_machine to modify the mcount function to call another function
> called "ftrace_record_ip". This new function will record in a preallocated
> hash (allocated by the ftrace initializer) all the callers of mcount. A
> check is made to see if the caller has already been put into the hash, and
> if so, it is not recorded again.
>
> Later on a kernel thread ftraced is created. This kernel thread wakes up
> once a second and checks to see if any new functions were added to the
> hash. If so, it then calls kstop_machine and modifies those callers to
> mcount into nops.

It will suffice to make it freezable, so that it doesn't run while the
system is suspending and resuming.

Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
 kernel/trace/ftrace.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 639e16c..49f4c3f 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -819,8 +819,13 @@ static int ftraced(void *ignore)
 {
 	unsigned long usecs;
 
+	set_freezable();
+
 	while (!kthread_should_stop()) {
 
+		if (try_to_freeze())
+			continue;
+
 		set_current_state(TASK_INTERRUPTIBLE);
 
 		/* check once a second */
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/