Messages in this thread Patch in this message | | | Date | Fri, 22 Aug 2008 06:46:49 +0200 | From | Ingo Molnar <> | Subject | Re: ftraced and suspend to ram |
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* Rafael J. Wysocki <rjw@sisk.pl> wrote:
> > > The code in question is the ftraced() function in > > > kernel/trace/ftrace.c > > > > Thanks, I'll have a look in a while. > > Can you try the appended patch, please?
makes sense - i've applied it to tip/tracing/urgent, see the tidied up commit below.
It should be no big issue not being able to trace across suspend+resume - and that restriction will go away with Steve's build-time based mcount patching mechanism in v2.6.28.
Ingo
-------------> From 0e556695ddc8eebf6f6dd86bb0c4911b2b90c12a Mon Sep 17 00:00:00 2001 From: Rafael J. Wysocki <rjw@sisk.pl> Date: Thu, 21 Aug 2008 21:59:36 +0200 Subject: [PATCH] ftrace: fix ftraced and suspend to ram
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@elte.hu> --- 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 */
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