Thank Thomas for your guidance On Sun, Nov 27, 2022 at 1:05 AM Thomas Gleixner <t...@linutronix.de> wrote: > > 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? Yes, this is a false positive instead. > > > 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'... Documentation/process/submitting-patches.rst says: "Describe your changes in imperative mood, e.g. "make xyzzy do frotz" instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy to do frotz", as if you are giving orders to the codebase to change its behaviour."
So, I should construct my patch as: We avoid ... by ... > > > > > Signed-off-by: Zhouyi Zhou <zhouzho...@gmail.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. I am going to do a study on this, for now, I do a grep in the kernel tree: find . -name "*.c"|xargs grep cpuhp_setup_state|wc -l The result of the grep command shows that there are 268 cpuhp_setup_state* cases. which may make our task more complicated. After my study, should we also take Frederic's proposal as a possible option? (construct a function for this) https://lore.kernel.org/lkml/20221123223658.GC1395324@lothringen/ I learned a lot during this process Many thanks Zhouyi > > Thanks, > > tglx