[REGRESSION] PM / sleep: Unbalanced suspend/resume on late abort causes data abort

[Rose Wu <ya-jou.wu@mediatek.com>]

Hi Rafael and All,

I am reporting a regression introduced by the commit
443046d1ad66607f324c604b9fbdf11266fa8aad (PM: sleep: Make suspend of
devices more asynchronous), which can lead to a kernel panic (data
abort) if a late suspend aborts.
The commit modifies list handling during suspend. When a device suspend
aborts at the "late" stage, `dpm_suspended_list` is spliced into
`dpm_late_early_list`.
This creates an imbalance. Devices on this list that had not yet
executed `pm_runtime_disable()` in `device_suspend_late()` are now
incorrectly subjected to `pm_runtime_enable()` during the subsequent
`device_resume_early()` sequence.

This causes two issues:

1. Numerous error messages in dmesg: "Attempt to enable runtime PM when
it is blocked."
2. A critical failure for simple-bus devices: When
`simple_pm_bus_runtime_resume()` is called for a device whose bus is
`NULL`, the kernel attempts to access the null bus struct, triggering a
data abort.

Steps to Reproduce:

The issue can be reliably reproduced by forcing a late suspend to
abort.

1. Apply the following modification to the `device_suspend_late()`
function to simulate a wakeup event:
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -1568,7 +1568,7 @@ static int device_suspend_late(struct device
*dev, pm_message_t state, bool asyn
 	if (async_error)
 		goto Complete;
 
-	if (pm_wakeup_pending()) {
+	if (1) { /* Force abort for testing */
 		async_error = -EBUSY;
 		goto Complete;
 	}
2. Trigger a system suspend.
3. The system will attempt to suspend, abort at the late stage, and
then trigger the data abort during the resume sequence.

Call Trace:

Unable to handle kernel NULL pointer dereference at virtual address
0000000000000008
pc : [0xffffffe3988e81e4] simple_pm_bus_runtime_resume+0x1c/0x90
lr : [0xffffffe398a848d0] pm_generic_runtime_resume+0x40/0x58

As a potential fix, I am wondering if a conditional check is needed in
`device_resume_early()` before invoking `pm_runtime_enable()` for a
device?

Best Regards,
Rose