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 <[email protected]> > Signed-off-by: Sebastian Andrzej Siewior <[email protected]> > --- > 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
