linux-kernel - [PATCH 4.4 23/31] PM / sleep: dont suspend parent when async child suspend

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Message-Id: <20161124145448.147227847@linuxfoundation.org>
Date:   Thu, 24 Nov 2016 15:55:44 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jeffy Chen <jeffy.chen@...k-chips.com>,
        Brian Norris <briannorris@...omium.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: [PATCH 4.4 23/31] PM / sleep: dont suspend parent when async child suspend_{noirq, late} fails

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Brian Norris <briannorris@...omium.org>

commit 6f75c3fd56daf547d684127a7f83c283c3c160d1 upstream.

Consider two devices, A and B, where B is a child of A, and B utilizes
asynchronous suspend (it does not matter whether A is sync or async). If
B fails to suspend_noirq() or suspend_late(), or is interrupted by a
wakeup (pm_wakeup_pending()), then it aborts and sets the async_error
variable. However, device A does not (immediately) check the async_error
variable; it may continue to run its own suspend_noirq()/suspend_late()
callback. This is bad.

We can resolve this problem by doing our error and wakeup checking
(particularly, for the async_error flag) after waiting for children to
suspend, instead of before. This also helps align the logic for the noirq and
late suspend cases with the logic in __device_suspend().

It's easy to observe this erroneous behavior by, for example, forcing a
device to sleep a bit in its suspend_noirq() (to ensure the parent is
waiting for the child to complete), then return an error, and watch the
parent suspend_noirq() still get called. (Or similarly, fake a wakeup
event at the right (or is it wrong?) time.)

Fixes: de377b397272 (PM / sleep: Asynchronous threads for suspend_late)
Fixes: 28b6fd6e3779 (PM / sleep: Asynchronous threads for suspend_noirq)
Reported-by: Jeffy Chen <jeffy.chen@...k-chips.com>
Signed-off-by: Brian Norris <briannorris@...omium.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/base/power/main.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -1022,6 +1022,8 @@ static int __device_suspend_noirq(struct
 	TRACE_DEVICE(dev);
 	TRACE_SUSPEND(0);

+	dpm_wait_for_children(dev, async);
+
 	if (async_error)
 		goto Complete;

@@ -1033,8 +1035,6 @@ static int __device_suspend_noirq(struct
 	if (dev->power.syscore || dev->power.direct_complete)
 		goto Complete;

-	dpm_wait_for_children(dev, async);
-
 	if (dev->pm_domain) {
 		info = "noirq power domain ";
 		callback = pm_noirq_op(&dev->pm_domain->ops, state);
@@ -1169,6 +1169,8 @@ static int __device_suspend_late(struct

 	__pm_runtime_disable(dev, false);

+	dpm_wait_for_children(dev, async);
+
 	if (async_error)
 		goto Complete;

@@ -1180,8 +1182,6 @@ static int __device_suspend_late(struct
 	if (dev->power.syscore || dev->power.direct_complete)
 		goto Complete;

-	dpm_wait_for_children(dev, async);
-
 	if (dev->pm_domain) {
 		info = "late power domain ";
 		callback = pm_late_early_op(&dev->pm_domain->ops, state);