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    Subject[PATCH 5/8] nohz: Fix notifier return val that enforce timekeeping
    Date
    From: Li Zhong <zhong@linux.vnet.ibm.com>

    In tick_nohz_cpu_down_callback() if the cpu is the one handling
    timekeeping , we must return something that stops the CPU_DOWN_PREPARE
    notifiers and then start notify CPU_DOWN_FAILED on the already called
    notifier call backs.

    However traditional errno values are not handled by the notifier unless
    these are encapsulated using errno_to_notifier().

    Hence the current -EINVAL is misinterpreted and converted to junk after
    notifier_to_errno(), leaving the notifier subsystem to random behaviour
    such as eventually allowing the cpu to go down.

    Fix this by using the standard NOTIFY_BAD instead.

    Signed-off-by: Li Zhong <zhong@linux.vnet.ibm.com>
    Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Ingo Molnar <mingo@kernel.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Borislav Petkov <bp@alien8.de>
    Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
    ---
    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 cfc798b..58d8d4d 100644
    --- a/kernel/time/tick-sched.c
    +++ b/kernel/time/tick-sched.c
    @@ -311,7 +311,7 @@ static int __cpuinit tick_nohz_cpu_down_callback(struct notifier_block *nfb,
    * we can't safely shutdown that CPU.
    */
    if (have_nohz_full_mask && tick_do_timer_cpu == cpu)
    - return -EINVAL;
    + return NOTIFY_BAD;
    break;
    }
    return NOTIFY_OK;
    --
    1.7.5.4


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