On 01/21/2016 02:54 PM, Sebastian Andrzej Siewior wrote:
> * Mike Galbraith | 2016-01-19 03:29:57 [+0100]:
>
>>> And this is a new piece. So you forbid that tasks leave the CPU if
>>> lazy_count > 0. Let me look closed why this is happening and if this is
>>> v4.1 … v4.4 or not.
>>
>> We should probably just add the lazy bits to preemptible().
>
> Subject: preempt-lazy: Add the lazy-preemption check to preempt_schedule()
>
> Probably in the rebase onto v4.1 this check got moved into less commonly used
> preempt_schedule_notrace(). This patch ensures that both functions use it.
>
> Reported-by: Mike Galbraith <umgwanakikbuti@xxxxxxxxx>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> ---
> kernel/sched/core.c | 36 ++++++++++++++++++++++++++++--------
> 1 file changed, 28 insertions(+), 8 deletions(-)
>
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3461,6 +3461,30 @@ static void __sched notrace preempt_sche
> } while (need_resched());
> }
>
> +#ifdef CONFIG_PREEMPT_LAZY
> +/*
> + * If TIF_NEED_RESCHED is then we allow to be scheduled away since this is
> + * set by a RT task. Oterwise we try to avoid beeing scheduled out as long as
> + * preempt_lazy_count counter >0.
> + */
> +static int preemptible_lazy(void)
> +{
> + if (test_thread_flag(TIF_NEED_RESCHED))
> + return 1;
> + if (current_thread_info()->preempt_lazy_count)
> + return 0;
> + return 1;
> +}
> +
> +#else
> +
> +static int preemptible_lazy(void)
> +{
> + return 1;
> +}
> +
> +#endif
> +
> #ifdef CONFIG_PREEMPT
> /*
> * this is the entry point to schedule() from in-kernel preemption
> @@ -3475,6 +3499,8 @@ asmlinkage __visible void __sched notrac
> */
> if (likely(!preemptible()))
> return;
> + if (!preemptible_lazy())
> + return;
>
> preempt_schedule_common();
> }
> @@ -3501,15 +3527,9 @@ asmlinkage __visible void __sched notrac
>
> if (likely(!preemptible()))
> return;
> -
> -#ifdef CONFIG_PREEMPT_LAZY
> - /*
> - * Check for lazy preemption
> - */
> - if (current_thread_info()->preempt_lazy_count &&
> - !test_thread_flag(TIF_NEED_RESCHED))
> + if (!preemptible_lazy())
> return;
> -#endif
> +
> do {
> preempt_disable_notrace();
> /*
I can see below backtrace during boot if i backport this change in K4.1-rt
TI am437x-idk (UP) board.
[ 0.204022] Switched to clocksource arm_global_timer
[ 0.211982] ------------[ cut here ]------------
[ 0.212021] WARNING: CPU: 0 PID: 3 at kernel/softirq.c:894 __tasklet_action+0x150/0x17c()
[ 0.212027] Modules linked in:
[ 0.212041] CPU: 0 PID: 3 Comm: ksoftirqd/0 Not tainted 4.1.15-rt11-00324-g52f8148-dirty #117
[ 0.212046] Hardware name: Generic AM43 (Flattened Device Tree)
[ 0.212052] Backtrace:
[ 0.212080] [<c0012b50>] (dump_backtrace) from [<c0012d70>] (show_stack+0x18/0x1c)
[ 0.212085] r7:c0730a84 r6:0000037e r5:00000009 r4:00000000
[ 0.212112] [<c0012d58>] (show_stack) from [<c05e6940>] (dump_stack+0x20/0x28)
[ 0.212124] [<c05e6920>] (dump_stack) from [<c003713c>] (warn_slowpath_common+0x7c/0xb4)
[ 0.212134] [<c00370c0>] (warn_slowpath_common) from [<c0037218>] (warn_slowpath_null+0x24/0x2c)
[ 0.212138] r8:000f4240 r7:00000000 r6:c0841238 r5:00000018 r4:00000006
[ 0.212156] [<c00371f4>] (warn_slowpath_null) from [<c003a0a4>] (__tasklet_action+0x150/0x17c)
[ 0.212165] [<c0039f54>] (__tasklet_action) from [<c003a138>] (tasklet_action+0x30/0x38)
[ 0.212169] r9:04208140 r8:c0862300 r7:000000c0 r6:c082d774 r5:00000018 r4:00000006
[ 0.212187] [<c003a108>] (tasklet_action) from [<c0039c2c>] (do_current_softirqs+0x190/0x258)
[ 0.212197] [<c0039a9c>] (do_current_softirqs) from [<c003a170>] (run_ksoftirqd+0x30/0x58)
[ 0.212201] r10:00000000 r9:00000000 r8:00000002 r7:c082d8f0 r6:00000001 r5:ee81f740
[ 0.212213] r4:ee874000
[ 0.212227] [<c003a140>] (run_ksoftirqd) from [<c00534e0>] (smpboot_thread_fn+0x15c/0x278)
[ 0.212242] [<c0053384>] (smpboot_thread_fn) from [<c00500fc>] (kthread+0xcc/0xe4)
[ 0.212246] r9:00000000 r8:00000000 r7:c0053384 r6:ee81f740 r5:ee81f780 r4:00000000
[ 0.212265] [<c0050030>] (kthread) from [<c000f988>] (ret_from_fork+0x14/0x2c)
[ 0.212269] r7:00000000 r6:00000000 r5:c0050030 r4:ee81f780
[ 0.212279] ---[ end trace 0000000000000001 ]---
[ 0.212284] softirq: ================== c037d4c4 <---- t->func
^^
# grep c037d4c4 System.map
c037d4c4 t kbd_bh
--
regards,
-grygorii
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