Re: [Question] about patch: don't use [delayed_]work_pending()

From: Tejun Heo
Date: Fri Sep 02 2016 - 10:21:09 EST


On Fri, Sep 02, 2016 at 09:50:07AM -0400, Tejun Heo wrote:
> Hello,
>
> On Fri, Sep 02, 2016 at 09:17:04AM +0800, qiaozhou wrote:
> > > > I don't know whether it's meaningful to still check pending work here, or
> > > > it's not suggested to use pm_qos_update_request in this early boot up phase.
> > > > Could you help to share some opinions? (I can fix this issue by adding the
> > > > current qos value directly instead of default value, though.)
> > > Hmmm... but I suppose this is super-early in the boot. Would it make
> > > sense to have a static variable (e.g. bool clk_fully_initailized) to
> > > gate the cancel_delayed_sync() call?
> >
> > You're right that it's indeed super-early stage. But currently we can't
> > control the gate of can_delayed_work_sync, since it's inside
> > pm_qos_update_request. Out of our control. We can choose to not call
> > pm_qos_update_request to avoid this issue, and use pm_qos_add_request
> > alternatively. Good to have it.
>
> Ah sorry, didn't understand that the offending cancel_sync call is in
> the generic part. Hmm... but yeah, we should still be able to take
> the same approach. I'll see what's the right thing to gate the
> operation there.

Does the following patch work?

Subject: power: avoid calling cancel_delayed_work_sync() during early boot

of_clk_init() ends up calling into pm_qos_update_request() very early
during boot where irq is expected to stay disabled.
pm_qos_update_request() uses cancel_delayed_work_sync() which
correctly assumes that irq is enabled on invocation and
unconditionally disables and re-enables it.

Gate cancel_delayed_work_sync() invocation with kevented_up() to avoid
enabling irq unexpectedly during early boot.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Reported-by: Qiao Zhou <qiaozhou@xxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/d2501c4c-8e7b-bea3-1b01-000b36b5dfe9@xxxxxxxxxxxx
---
kernel/power/qos.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/power/qos.c b/kernel/power/qos.c
index 97b0df7..168ff44 100644
--- a/kernel/power/qos.c
+++ b/kernel/power/qos.c
@@ -482,7 +482,16 @@ void pm_qos_update_request(struct pm_qos_request *req,
return;
}

- cancel_delayed_work_sync(&req->work);
+ /*
+ * This function may be called very early during boot, for example,
+ * from of_clk_init(), where irq needs to stay disabled.
+ * cancel_delayed_work_sync() assumes that irq is enabled on
+ * invocation and re-enables it on return. Avoid calling it until
+ * workqueue is initialized.
+ */
+ if (keventd_up())
+ cancel_delayed_work_sync(&req->work);
+
__pm_qos_update_request(req, new_value);
}
EXPORT_SYMBOL_GPL(pm_qos_update_request);