Re: [PATCH 7/7] Revert "rtc: cmos: Replace spin_lock_irqsave with spin_lock in hard IRQ"

[Alexandre Belloni <alexandre.belloni@bootlin.com>]

On 14/09/2021 11:02:55+0300, Ville Syrjälä wrote:
> On Sun, Sep 12, 2021 at 02:42:14PM +0200, Mateusz Jończyk wrote:
> > Revert
> > commit 6950d046eb6e ("rtc: cmos: Replace spin_lock_irqsave with spin_lock in hard IRQ")
> > and add a comment.
> > 
> > As described in a previous
> > commit 66e4f4a9cc38 ("rtc: cmos: Use spin_lock_irqsave() in cmos_interrupt()")
> > from February 2020:
> > 
> >         cmos_interrupt() isn't always called from hardirq context, so
> >         we must use spin_lock_irqsave() & co.
> > 
> > Indeed, cmos_interrupt() is called from cmos_check_wkalrm(), which is
> > called from cmos_resume() - apparently not in an interrupt context.
> > 
> > A later
> > commit 6950d046eb6e ("rtc: cmos: Replace spin_lock_irqsave with spin_lock in hard IRQ")
> > did not take account of this and changed spin_lock_irqsave() to spin_lock().
> > This may cause a deadlock as quoted in the body of
> > commit 66e4f4a9cc38 ("rtc: cmos: Use spin_lock_irqsave() in cmos_interrupt()")
> > mentioned earlier.
> 
> This regression was supposed to be fixed by
> https://lore.kernel.org/linux-rtc/20210305122140.28774-1-chris@chris-wilson.co.uk/
> 
> What happened to that one? I don't see it in Linus's tree...
> 

Yes, that's exactly what I was wondering when seeing that patch and it
still sits in my rtc-fixes branch that I forgot to send to Linus...

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com