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SubjectRe: ftraced and suspend to ram
Date
On Thursday, 21 of August 2008, Rafael J. Wysocki wrote:
> On Thursday, 21 of August 2008, Steven Rostedt wrote:
> >
> > On Thu, 21 Aug 2008, Rafael J. Wysocki wrote:
> >
> > > On Thursday, 21 of August 2008, Steven Rostedt wrote:
> > > >
> > > > 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.
> > > >
> > > > Again, this daemon method makes resume from suspend to ram reboot instead
> > > > of resuming. Now, I'm asking the s2r gurus, what did I miss? Do I need to
> > > > add a "NO_FREEZE" flag or something to the "ftraced" kernel thread?
> > > >
> > > > Just asking for some advice.
> > >
> > > If I'm not mistaken, it'll probably suffice to make it freezable, so that it
> > > doesn't run while the system is suspending and resuming. Would that be
> > > acceptable?
> >
> > Does it not freeze by default.
>
> No, it doesn't. Kernel threads are not freezable by default
>
> > > Please tell me where exactly the ftraced source code is located.
> >
> > It's in Linus's latest git tree.
> >
> > 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?

Thanks,
Rafael

---
kernel/trace/ftrace.c | 5 +++++
1 file changed, 5 insertions(+)
Index: linux-2.6/kernel/trace/ftrace.c
===================================================================
--- linux-2.6.orig/kernel/trace/ftrace.c
+++ linux-2.6/kernel/trace/ftrace.c
@@ -796,8 +796,13 @@ 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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