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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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      Last update: 2008-08-21 21:59    [W:0.025 / U:0.936 seconds]
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