From: Phil Auld pauld@redhat.com
[ Upstream commit 64ea6e44f85b9b75925ebe1ba0e6e8430cc4e06f ]
Writing the current state back in hotplug/target calls cpu_down() which will set cpu dying even when it isn't and then nothing will ever clear it. A stress test that reads values and writes them back for all cpu device files in sysfs will trigger the BUG() in select_fallback_rq once all cpus are marked as dying.
kernel/cpu.c::target_store() ... if (st->state < target) ret = cpu_up(dev->id, target); else ret = cpu_down(dev->id, target);
cpu_down() -> cpu_set_state() bool bringup = st->state < target; ... if (cpu_dying(cpu) != !bringup) set_cpu_dying(cpu, !bringup);
Fix this by letting state==target fall through in the target_store() conditional. Also make sure st->target == target in that case.
Fixes: 757c989b9994 ("cpu/hotplug: Make target state writeable") Signed-off-by: Phil Auld pauld@redhat.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Reviewed-by: Valentin Schneider vschneid@redhat.com Link: https://lore.kernel.org/r/20221117162329.3164999-2-pauld@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/cpu.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/cpu.c b/kernel/cpu.c index 3c9ee966c56a..008b50da2224 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -2231,8 +2231,10 @@ static ssize_t write_cpuhp_target(struct device *dev,
if (st->state < target) ret = cpu_up(dev->id, target); - else + else if (st->state > target) ret = cpu_down(dev->id, target); + else if (WARN_ON(st->target != target)) + st->target = target; out: unlock_device_hotplug(); return ret ? ret : count;