* [RESEND PATCH v4 0/2] cpuhp: fix some st->target issues
@ 2022-09-15 15:37 Phil Auld
2022-09-15 15:37 ` [RESEND PATCH v4 1/2] cpuhp: make target_store() a nop when target == state Phil Auld
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: Phil Auld @ 2022-09-15 15:37 UTC (permalink / raw)
To: linux-kernel
Cc: Thomas Gleixner, Peter Zijlstra, Valentin Schneider,
Steven Price, Mark Rutland, Frederic Weisbecker
Fix a couple of 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.
v4: Use WARN_ON in the case where state == target but st->target does
not.
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
^ permalink raw reply [flat|nested] 4+ messages in thread
* [RESEND PATCH v4 1/2] cpuhp: make target_store() a nop when target == state
2022-09-15 15:37 [RESEND PATCH v4 0/2] cpuhp: fix some st->target issues Phil Auld
@ 2022-09-15 15:37 ` Phil Auld
2022-09-15 15:37 ` [RESEND PATCH v4 2/2] cpuhp: Set cpuhp target for boot cpu Phil Auld
2022-10-03 14:11 ` [RESEND PATCH v4 0/2] cpuhp: fix some st->target issues Phil Auld
2 siblings, 0 replies; 4+ messages in thread
From: Phil Auld @ 2022-09-15 15:37 UTC (permalink / raw)
To: linux-kernel
Cc: Thomas Gleixner, Peter Zijlstra, Valentin Schneider,
Steven Price, Mark Rutland, Frederic Weisbecker
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 <pauld@redhat.com>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Fixes: 757c989b9994 ("cpu/hotplug: Make target state writeable")
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Frederic Weisbecker <frederic@kernel.org>
---
kernel/cpu.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index bbad5e375d3b..979de993f853 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 (WARN_ON(st->target != target))
+ st->target = target;
out:
unlock_device_hotplug();
return ret ? ret : count;
--
2.31.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* [RESEND PATCH v4 2/2] cpuhp: Set cpuhp target for boot cpu
2022-09-15 15:37 [RESEND PATCH v4 0/2] cpuhp: fix some st->target issues Phil Auld
2022-09-15 15:37 ` [RESEND PATCH v4 1/2] cpuhp: make target_store() a nop when target == state Phil Auld
@ 2022-09-15 15:37 ` Phil Auld
2022-10-03 14:11 ` [RESEND PATCH v4 0/2] cpuhp: fix some st->target issues Phil Auld
2 siblings, 0 replies; 4+ messages in thread
From: Phil Auld @ 2022-09-15 15:37 UTC (permalink / raw)
To: linux-kernel
Cc: Thomas Gleixner, Peter Zijlstra, Valentin Schneider,
Steven Price, Mark Rutland, Frederic Weisbecker
Since the boot cpu does not go through the hotplug process it ends
up with state == CPUHP_ONLINE but target == CPUHP_OFFLINE.
So set the target to match in boot_cpu_hotplug_init().
Signed-off-by: Phil Auld <pauld@redhat.com>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Frederic Weisbecker <frederic@kernel.org>
---
kernel/cpu.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 979de993f853..3f704a8896b0 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
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [RESEND PATCH v4 0/2] cpuhp: fix some st->target issues
2022-09-15 15:37 [RESEND PATCH v4 0/2] cpuhp: fix some st->target issues Phil Auld
2022-09-15 15:37 ` [RESEND PATCH v4 1/2] cpuhp: make target_store() a nop when target == state Phil Auld
2022-09-15 15:37 ` [RESEND PATCH v4 2/2] cpuhp: Set cpuhp target for boot cpu Phil Auld
@ 2022-10-03 14:11 ` Phil Auld
2 siblings, 0 replies; 4+ messages in thread
From: Phil Auld @ 2022-10-03 14:11 UTC (permalink / raw)
To: linux-kernel
Cc: Thomas Gleixner, Peter Zijlstra, Valentin Schneider,
Steven Price, Mark Rutland, Frederic Weisbecker
On Thu, Sep 15, 2022 at 11:37:49AM -0400 Phil Auld wrote:
> Fix a couple of 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.
>
> v4: Use WARN_ON in the case where state == target but st->target does
> not.
>
> 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
>
Pingy McPing-face :)
Peter? Anyone? It's really not ideal to have a cpu marked dying when
it isn't actually going down. Please take a look.
Thanks for your time.
Cheers,
Phil
--
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2022-10-03 14:12 UTC | newest]
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