linux-kernel - Re: [PATCH v2 2/2] alarmtimer: Modify alarmtimer suspend callback to check for imminent alarm using PM notifier

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Date: Tue, 13 Feb 2024 20:30:28 +0000
From: Pranav Prasad <pranavpp@...gle.com>
To: tglx@...utronix.de, jstultz@...gle.com, sboyd@...nel.org
Cc: linux-kernel@...r.kernel.org, krossmo@...gle.com
Subject: Re: [PATCH v2 2/2] alarmtimer: Modify alarmtimer suspend callback to
 check for imminent alarm using PM notifier

> Why is this a warning? If at all it wants to be pr_debug() and the
> __func_ is pretty useless as grep is able to find the string, no?

Agreed with the pr_debug(), doesn't need to be a warning. I had
made it a warning so that it is logged by default (KERN_WARN),
so that it can grepped for without enabling dynamic debug for this
module.

> How is this supposed to work? rtc is NULL.

alarmtimer_get_soonest() has the following:
	rtc = alarmtimer_get_rtcdev();
        if (!rtc)
		return 0;

rtc is set in alarmtimer_get_soonest(). If rtc is NULL, the notifier
returns NOTIFY_DONE before even reaching pm_wakeup_event(), hence there is
no NULL pointer dereference expected.

I agree that I should move it out of alarmtimer_get_soonest() and assign
it before the function call as it is unrelated to getting the soonest
alarm.

> How was this ever tested?

I tested it by forcing kernel suspend writing 'mem' to /sys/power/state and
using a large window (120s instead of the current 2s) so that a pending
alarm is likely. The debug print is logged as expected without any kernel
crash, and the suspend gets aborted.

Thanks for the other comments, Thomas and John!
I shall send out a v3 with all the fixes.

Regards,
Pranav