[PATCH 2/2] PM / sleep: don't suspend parent when async child suspend_{noirq,early} fails

From: Brian Norris
Date: Wed Oct 19 2016 - 20:27:14 EST

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_early(), 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_early()
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@xxxxxxxxxxxxxx>
Signed-off-by: Brian Norris <briannorris@xxxxxxxxxxxx>
Tested mostly on 4.4, but the code (and seemingly the bug) is mostly untouched
since then. I can try to conjure up a proper upstream test if required.

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);