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 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.

thanks,

greg k-h