linux-kernel - [PATCH v2 2/2] PM / sleep: don't suspend parent when async child suspend

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Message-Id: <1477584334-39956-1-git-send-email-briannorris@chromium.org>
Date:   Thu, 27 Oct 2016 09:05:34 -0700
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 v2 2/2] 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 checking the async_error flag after
waiting for children to suspend, using the same logic for the noirq and
late suspend cases as we already do for __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>
Reviewed-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
---
v2: s/early/late/ in commit message

 drivers/base/power/main.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index c58563581345..eaf6b53463a5 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -1040,6 +1040,9 @@ static int __device_suspend_noirq(struct device *dev, pm_message_t state, bool a

 	dpm_wait_for_children(dev, async);

+	if (async_error)
+		goto Complete;
+
 	if (dev->pm_domain) {
 		info = "noirq power domain ";
 		callback = pm_noirq_op(&dev->pm_domain->ops, state);
@@ -1187,6 +1190,9 @@ static int __device_suspend_late(struct device *dev, pm_message_t state, bool as

 	dpm_wait_for_children(dev, async);

+	if (async_error)
+		goto Complete;
+
 	if (dev->pm_domain) {
 		info = "late power domain ";
 		callback = pm_late_early_op(&dev->pm_domain->ops, state);
-- 
2.8.0.rc3.226.g39d4020