Messages in this thread Patch in this message | | | From | "Rafael J. Wysocki" <> | Subject | Re: ftraced and suspend to ram | Date | Thu, 21 Aug 2008 21:59:36 +0200 |
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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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