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Subject[PATCH v3] PM / sleep: don't suspend parent when async child suspend_{noirq,late} fails
Date
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@rock-chips.com>
Signed-off-by: Brian Norris <briannorris@chromium.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
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