linux-kernel - [PATCH] PM / QoS: Fix workqueue deadlock when using pm_qos_update_request

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Date:	Thu,  8 Aug 2013 13:13:57 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>
Subject: [PATCH] PM / QoS: Fix workqueue deadlock when using pm_qos_update_request_timeout()

pm_qos_update_request_timeout() updates a qos and then schedules
a delayed work item to bring the qos back down to the default
after the timeout. When the work item runs, pm_qos_work_fn() will
call pm_qos_update_request() and deadlock because it tries to
cancel itself via cancel_delayed_work_sync(). Future callers of
that qos will also hang waiting to cancel the work that is
canceling itself. Before ed1ac6e (PM: don't use
[delayed_]work_pending(), 2013-01-11) this didn't happen because
the work function wouldn't try to cancel itself.

Let's just do the little bit of pm_qos_update_request() here so
that we don't deadlock.

Cc: Tejun Heo <tj@...nel.org>
Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
---
 kernel/power/qos.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/power/qos.c b/kernel/power/qos.c
index 06fe285..d52d314 100644
--- a/kernel/power/qos.c
+++ b/kernel/power/qos.c
@@ -308,7 +308,11 @@ static void pm_qos_work_fn(struct work_struct *work)
 						  struct pm_qos_request,
 						  work);

-	pm_qos_update_request(req, PM_QOS_DEFAULT_VALUE);
+	if (PM_QOS_DEFAULT_VALUE != req->node.prio)
+		pm_qos_update_target(
+				pm_qos_array[req->pm_qos_class]->constraints,
+				&req->node, PM_QOS_UPDATE_REQ,
+				PM_QOS_DEFAULT_VALUE);
 }

 /**
-- 
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