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

Bugzilla: https://bugzilla.redhat.com/2086305

commit 64ea6e44f85b9b75925ebe1ba0e6e8430cc4e06f
Author: Phil Auld <pauld@redhat.com>
Date:   Thu Nov 17 11:23:28 2022 -0500

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

    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: 757c989b99 ("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: Phil Auld <pauld@redhat.com>
This commit is contained in:
Phil Auld 2023-01-04 09:38:36 -05:00
parent b2e062f7be
commit e6bfcc76c9
1 changed files with 3 additions and 1 deletions
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4
kernel/cpu.c
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@ -2292,8 +2292,10 @@ 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;