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cpu/hotplug: Make target_store() a nop when target == state

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[ 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>
This commit is contained in:
Phil Auld 2022-11-17 11:23:28 -05:00 committed by Greg Kroah-Hartman
parent fc89b8853a
commit 270700e7df
1 changed files with 3 additions and 1 deletions
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4
kernel/cpu.c
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@ -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;