linux-kernel - [PATCH v3] PM / sleep: don't suspend parent when async child suspend

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Date:   Wed,  9 Nov 2016 17:21:08 -0800
From:   Brian Norris <briannorris@...omium.org>
To:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     <linux-kernel@...r.kernel.org>,
        Doug Anderson <dianders@...omium.org>,
        Brian Norris <computersforpeace@...il.com>,
        Jeffy Chen <jeffy.chen@...k-chips.com>,
        linux-pm@...r.kernel.org,
        Chuansheng Liu <chuansheng.liu@...el.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Brian Norris <briannorris@...omium.org>
Subject: [PATCH v3] PM / sleep: don't suspend parent when async child suspend_{noirq,late} fails

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>
---
v2: s/early/late/ in commit message

v3:
 * drop patch 1, as the callback-printing is unrelated, semi-controversial, and
   might break existing (but poor -- c'mon, since when do tools get to rely on
   kernel messages?) tools
 * do all error checking after dpm_wait_for_children() -- this helps make
   things consistent and reduces duplication.
 * drop Dmitry's Reviewed-by, since the patch changed enough

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

diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index c58563581345..57a8ca4bc8ab 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -1027,6 +1027,8 @@ static int __device_suspend_noirq(struct device *dev, pm_message_t state, bool a
 	TRACE_DEVICE(dev);
 	TRACE_SUSPEND(0);

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

@@ -1038,8 +1040,6 @@ static int __device_suspend_noirq(struct device *dev, pm_message_t state, bool a
 	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);
@@ -1174,6 +1174,8 @@ static int __device_suspend_late(struct device *dev, pm_message_t state, bool as

 	__pm_runtime_disable(dev, false);

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

@@ -1185,8 +1187,6 @@ static int __device_suspend_late(struct device *dev, pm_message_t state, bool as
 	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);
-- 
2.8.0.rc3.226.g39d4020