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    SubjectRe: 2.6.25-rc2 rcupreempt WARN after suspend to ram
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    Am Dienstag, 26. Februar 2008 schrieb Karsten Wiese:
    > Am Sonntag, 24. Februar 2008 schrieb Paul E. McKenney:
    > > On Sun, Feb 24, 2008 at 04:38:15PM +0100, Karsten Wiese wrote:
    > > > Am Samstag, 23. Februar 2008 schrieb Karsten Wiese:
    > > > > Am Samstag, 23. Februar 2008 schrieb Paul E. McKenney:
    > > > > > On Sat, Feb 23, 2008 at 01:41:02PM +0100, Karsten Wiese wrote:
    > > > > > > Hi,
    > > > > > >
    > > > > > > This appeared in dmesg after
    > > > > > > $ echo core > /sys/power/pm_test
    > > > > > > followed by 3 cycles of
    > > > > > > $ echo mem > /sys/power/state
    > > > > > > . .config attached.
    > > > > > >
    > > > > > > dmesg excerpt (, full ~1MByte available):
    > > > > >
    > > > > > Does this tree have http://lkml.org/lkml/2008/1/29/208 applied?
    > > > >
    > > > > Yes. This tree was linus' git head as of yesterday or the day before.
    > > >
    > > > Updated to git-head of today, same test and .config, different symptoms
    > > > like in this thread: http://lkml.org/lkml/2008/2/23/260
    > > > Later in this thread, Alan Cox said it looked like irq problems.
    > > > Maybe also the rcupreemt related WARN_ON I saw are caused by irq problems.
    > >
    > > Might be, but am taking a closer look at the interaction between irq,
    > > dynticks, and rcupreempt in any case.
    >
    > [Added Rafael, Thomas and Steven to CC]
    >
    > The "different symptoms" above are indeed unrelated and solved by reverting
    > "commit 559bbe6cbd0d8c68d40076a5f7dc98e3bf5864b2
    > power_state: get rid of write-only variable in SATA"
    >
    > The cpu_hotplug code used by suspend together with hr_timer and nohz looks
    > suspicious:
    > $ echo 0 > /sys/devices/system/cpu/cpu1/online
    > $ echo 1 > /sys/devices/system/cpu/cpu1/online
    > (repeat until dmesg|tail shows WARNs; here it took 2 iterations)
    > causes symptoms like in 1st message of this thread again.

    [Added Andrew]

    This fixes it, not sure if its not just papering over, though it seams to be
    likely for an offlined CPU to have ticks stopped.

    Thanks,
    Karsten
    ---

    Don't touch an offlined CPU's ts->tick_stopped in tick_cancel_sched_timer()

    Silences WARN_ONs in rcu_enter_nohz() and rcu_exit_nohz(), which appeared
    before caused by (repeated) calls to:
    $ echo 0 > /sys/devices/system/cpu/cpu1/online
    $ echo 1 > /sys/devices/system/cpu/cpu1/online

    Signed-off-by: Karsten Wiese <fzu@wemgehoertderstaat.de>
    ---
    kernel/time/tick-sched.c | 2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)

    diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
    index 2968298..686da82 100644
    --- a/kernel/time/tick-sched.c
    +++ b/kernel/time/tick-sched.c
    @@ -640,7 +640,7 @@ void tick_cancel_sched_timer(int cpu)

    if (ts->sched_timer.base)
    hrtimer_cancel(&ts->sched_timer);
    - ts->tick_stopped = 0;
    +
    ts->nohz_mode = NOHZ_MODE_INACTIVE;
    }
    #endif /* HIGH_RES_TIMERS */
    --
    1.5.3.3


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