Several small fixes that clean up some cpuhp inconsistencies.
The first prevents target_store() from calling cpu_down() when
target == state which prevents the cpu being incorrectly marked
as dying. The second just makes the boot cpu have a valid cpuhp
target rather than 0 (CPU_OFFLINE) while being in state
CPU_ONLINE.
A further issue which these two patches don't address is that
the cpuX/online file looks at the device->offline state and can
thus get out of sync with the actual cpuhp state if the cpuhp
target is used to change state.
v3: Added code to make sure st->target == target in the nop case.
Phil Auld (2):
cpuhp: make target_store() a nop when target == state
cpuhp: Set cpuhp target for boot cpu
kernel/cpu.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
--
2.31.1
Since the boot cpu does not go through the hotplug process it ends
up with state == CPUHP_ONLINE but target == CPUHP_OFFLINE.
Set the target to match in boot_cpu_hotplug_init().
Signed-off-by: Phil Auld <[email protected]>
---
kernel/cpu.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 305694a2ca26..104f43a6f4ad 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -2690,6 +2690,7 @@ void __init boot_cpu_hotplug_init(void)
cpumask_set_cpu(smp_processor_id(), &cpus_booted_once_mask);
#endif
this_cpu_write(cpuhp_state.state, CPUHP_ONLINE);
+ this_cpu_write(cpuhp_state.target, CPUHP_ONLINE);
}
/*
--
2.31.1
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.
Signed-off-by: Phil Auld <[email protected]>
---
kernel/cpu.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index bbad5e375d3b..305694a2ca26 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -2326,8 +2326,10 @@ static ssize_t target_store(struct device *dev, struct device_attribute *attr,
if (st->state < target)
ret = cpu_up(dev->id, target);
- else
+ else if (st->state > target)
ret = cpu_down(dev->id, target);
+ else if (st->target != target)
+ st->target = target;
out:
unlock_device_hotplug();
return ret ? ret : count;
--
2.31.1
On 11/07/22 17:16, Phil Auld wrote:
> 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.
>
> Signed-off-by: Phil Auld <[email protected]>
One nit below, otherwise:
Reviewed-by: Valentin Schneider <[email protected]>
> ---
> kernel/cpu.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index bbad5e375d3b..305694a2ca26 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -2326,8 +2326,10 @@ static ssize_t target_store(struct device *dev, struct device_attribute *attr,
>
> if (st->state < target)
> ret = cpu_up(dev->id, target);
> - else
> + else if (st->state > target)
> ret = cpu_down(dev->id, target);
> + else if (st->target != target)
Should we make this:
else if (WARN(st->target != target))
> + st->target = target;
> out:
> unlock_device_hotplug();
> return ret ? ret : count;
> --
> 2.31.1
On Tue, Jul 19, 2022 at 03:34:03PM +0100 Valentin Schneider wrote:
> On 11/07/22 17:16, Phil Auld wrote:
> > 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.
> >
> > Signed-off-by: Phil Auld <[email protected]>
>
> One nit below, otherwise:
> Reviewed-by: Valentin Schneider <[email protected]>
>
Thanks!
> > ---
> > kernel/cpu.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/cpu.c b/kernel/cpu.c
> > index bbad5e375d3b..305694a2ca26 100644
> > --- a/kernel/cpu.c
> > +++ b/kernel/cpu.c
> > @@ -2326,8 +2326,10 @@ static ssize_t target_store(struct device *dev, struct device_attribute *attr,
> >
> > if (st->state < target)
> > ret = cpu_up(dev->id, target);
> > - else
> > + else if (st->state > target)
> > ret = cpu_down(dev->id, target);
> > + else if (st->target != target)
>
> Should we make this:
>
> else if (WARN(st->target != target))
>
If you think that's important I can make it a WARN, sure.
I'll try to remember to keep your Reviewed-bys this time if that's okay.
Cheers,
Phil
> > + st->target = target;
> > out:
> > unlock_device_hotplug();
> > return ret ? ret : count;
> > --
> > 2.31.1
>
--
On 11/07/22 17:16, Phil Auld wrote:
> Since the boot cpu does not go through the hotplug process it ends
> up with state == CPUHP_ONLINE but target == CPUHP_OFFLINE.
> Set the target to match in boot_cpu_hotplug_init().
>
> Signed-off-by: Phil Auld <[email protected]>
Reviewed-by: Valentin Schneider <[email protected]>
On Mon, Jul 11, 2022 at 05:16:17PM -0400 Phil Auld wrote:
> Several small fixes that clean up some cpuhp inconsistencies.
> The first prevents target_store() from calling cpu_down() when
> target == state which prevents the cpu being incorrectly marked
> as dying. The second just makes the boot cpu have a valid cpuhp
> target rather than 0 (CPU_OFFLINE) while being in state
> CPU_ONLINE.
>
> A further issue which these two patches don't address is that
> the cpuX/online file looks at the device->offline state and can
> thus get out of sync with the actual cpuhp state if the cpuhp
> target is used to change state.
>
> v3: Added code to make sure st->target == target in the nop case.
>
> Phil Auld (2):
> cpuhp: make target_store() a nop when target == state
> cpuhp: Set cpuhp target for boot cpu
>
> kernel/cpu.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> --
> 2.31.1
>
Ping?
Any thoughts on this? I'm not sure what tree it needs to go in but
getting a cpu shutdown by writing the current target/state back
in here seems wrong.
Thanks,
Phil
--