linux-kernel - [PATCH 3.16 221/306] PM / sleep: don't suspend parent when async child suspend

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Date:   Wed, 15 Feb 2017 22:41:40 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        "Jeffy Chen" <jeffy.chen@...k-chips.com>,
        "Brian Norris" <briannorris@...omium.org>
Subject: [PATCH 3.16 221/306] PM / sleep: don't suspend parent when async
 child suspend_{noirq, late} fails

3.16.40-rc1 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: Ben Hutchings <ben@...adent.org.uk>
---
 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
@@ -1014,6 +1014,8 @@ static int __device_suspend_noirq(struct
 	char *info = NULL;
 	int error = 0;

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

@@ -1025,8 +1027,6 @@ 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);
@@ -1155,6 +1155,8 @@ static int __device_suspend_late(struct

 	__pm_runtime_disable(dev, false);

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

@@ -1166,8 +1168,6 @@ 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);