linux-kernel - Crash introduced by commit b8b2c7d845d5 ("base/platform: assert that dev_pm_domain callbacks are called unconditionally")

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Date:	Tue, 19 Jan 2016 13:22:22 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
cc:	Linux-pm mailing list <linux-pm@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Crash introduced by commit b8b2c7d845d5 ("base/platform: assert that
 dev_pm_domain callbacks are called unconditionally")

Uwe:

Your commit causes my ASUS laptop to crash during early boot.  The 
problem occurs in platform_drv_probe(), affecting both the alarmtimer 
and the asus_laptop platform drivers (I can't tell which is the 
critical one).

The old code would not call platform_drv_probe() at all, and probing
would always succeed immediately because these drivers have no probe
routine.  But with the new code, platform_drv_probe() does run.  The
call to of_clk_set_defaults() returns -ENODEV, as does the call to
dev_pm_domain_attach().  The call to drv->probe() gets skipped, of 
course.  The final return value is -ENODEV, and so probing fails.  This 
causes the kernel to crash: blank screen, NumLock LED blinking.

The patch below fixes the problem, but I'm not sure that it's the best 
solution.  What is your advice?

Alan Stern

Index: usb-4.4/drivers/base/platform.c
===================================================================
--- usb-4.4.orig/drivers/base/platform.c
+++ usb-4.4/drivers/base/platform.c
@@ -524,6 +524,8 @@ static int platform_drv_probe(struct dev
 		ret = -ENXIO;
 	}

+	if (!drv->probe)
+		ret = 0;
 	return ret;
 }