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Message-ID: <87y1rxwsse.ffs@tglx> Date: Sat, 26 Nov 2022 18:05:05 +0100 From: Thomas Gleixner <tglx@...utronix.de> To: Zhouyi Zhou <zhouzhouyi@...il.com>, fweisbec@...il.com, mingo@...nel.org, dave@...olabs.net, paulmck@...nel.org, josh@...htriplett.org, mpe@...erman.id.au, linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org Cc: Zhouyi Zhou <zhouzhouyi@...il.com> Subject: Re: [PATCH linux-next][RFC]torture: avoid offline tick_do_timer_cpu On Mon, Nov 21 2022 at 11:51, Zhouyi Zhou wrote: > During CPU-hotplug torture (CONFIG_NO_HZ_FULL=y), if we try to > offline tick_do_timer_cpu, the operation will fail because in > function tick_nohz_cpu_down: > ``` > if (tick_nohz_full_running && tick_do_timer_cpu == cpu) > return -EBUSY; > ``` > Above bug was first discovered in torture tests performed in PPC VM How is this a bug? > of Open Source Lab of Oregon State University, and reproducable in RISC-V > and X86-64 (with additional kernel commandline cpu0_hotplug). > > In this patch, we avoid offline tick_do_timer_cpu by distribute > the offlining cpu among remaining cpus. Please read Documentation/process. Search for 'this patch'... > > Signed-off-by: Zhouyi Zhou <zhouzhouyi@...il.com> > --- > include/linux/tick.h | 1 + > kernel/time/tick-common.c | 1 + > kernel/time/tick-internal.h | 1 - > kernel/torture.c | 10 ++++++++++ > 4 files changed, 12 insertions(+), 1 deletion(-) > > diff --git a/include/linux/tick.h b/include/linux/tick.h > index bfd571f18cfd..23cc0b205853 100644 > --- a/include/linux/tick.h > +++ b/include/linux/tick.h > @@ -14,6 +14,7 @@ > #include <linux/rcupdate.h> > > #ifdef CONFIG_GENERIC_CLOCKEVENTS > +extern int tick_do_timer_cpu __read_mostly; > extern void __init tick_init(void); > /* Should be core only, but ARM BL switcher requires it */ > extern void tick_suspend_local(void); > diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c > index 46789356f856..87b9b9afa320 100644 > --- a/kernel/time/tick-common.c > +++ b/kernel/time/tick-common.c > @@ -48,6 +48,7 @@ ktime_t tick_next_period; > * procedure also covers cpu hotplug. > */ > int tick_do_timer_cpu __read_mostly = TICK_DO_TIMER_BOOT; > +EXPORT_SYMBOL_GPL(tick_do_timer_cpu); No. We are not exporting this just to make a bogus test case happy. Fix the torture code to handle -EBUSY correctly. Thanks, tglx
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