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'...
quoted hunk ↗ jump to hunk
Signed-off-by: Zhouyi Zhou <redacted>
---
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