Re: [PATCH 2/3] PM: add sysfs attributes for additional suspend/resume metrics

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Nov 10, 2026 at 01:54:05PM -0500, Greg Kroah-Hartman wrote:
> On Tue, Nov 10, 2026 at 07:50:20PM +0100, Joshua Crofts wrote:
> > On Tue, 10 Nov 2026 12:29:11 -0500
> > Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:
> > 
> > ...
> > 
> > > > +static ssize_t runtime_resume_count_show(struct device *dev,
> > > > +					 struct device_attribute *attr,
> > > > +					 char *buf)
> > > > +{
> > > > +	u64 count;
> > > > +
> > > > +	spin_lock_irq(&dev->power.lock);
> > > > +	count = dev->power.resume_count;
> > > > +	spin_unlock_irq(&dev->power.lock);  
> > > 
> > > Why is a lock needed at all?  The value isn't going to "smear", it will
> > > change right after the lock anyway.
> > 
> > On 64-bit systems an aligned u64 read is atomic, but on 32-bit systems it
> > gets split into two 32-bit loads. Without locking, the read can tear
> > between the upper and lower halves.
> 
> Are you sure?  ANd if so, is that so bad?  The value is "best effort" as
> it can, and will, change right after reading it.

And even more relevant, what specific 32bit system are you using that
this new api is going to be relying on?

thanks,

greg k-h