Re: [RFC PATCH v2 2/5] mm/show_mem: Avoid blocking on zone->lock during Oops or panic

[Aaron Tomlin]

On Wed, Nov 04, 2026 at 02:49:19AM +0000, sashiko-bot@xxxxxxxxxx wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] mm/show_mem: false lock contention warning in show_free_areas()
> --
> 
> commit e1c6e11316c0b99b2f700b8251c5ed2b76aad84a
> Author: Aaron Tomlin <atomlin@xxxxxxxxxxx>
> 
> mm/show_mem: Avoid blocking on zone->lock during Oops or panic
> 
> This commit updates show_free_areas() in mm/show_mem.c to avoid unconditionally calling spin_lock_irqsave() on zone->lock during Oops, panic, or NMI/atomic contexts, skipping zones when acquiring the lock is unsafe or contended.
> 
> > diff --git a/mm/show_mem.c b/mm/show_mem.c
> > index b938cbcd774a1..77098077523a9 100644
> > --- a/mm/show_mem.c
> > +++ b/mm/show_mem.c
> > @@ -367,10 +367,17 @@ static void show_free_areas(unsigned int filter, const nodemask_t *nodemask,
> >  			continue;
> >  		if (show_mem_node_skip(filter, zone_to_nid(zone), nodemask))
> >  			continue;
> > -		show_node(zone);
> > -		printk(KERN_CONT "%s: ", zone->name);
> >  
> > -		spin_lock_irqsave(&zone->lock, flags);
> > +		if (!can_spin_trylock() || in_nmi() ||
> > +		    oops_in_progress || panic_in_progress()) {
> > +			if (!can_spin_trylock() ||
> > +			    !spin_trylock_irqsave(&zone->lock, flags)) {
> > +				pr_warn("zone %s lock contended\n", zone->name);
> > +				continue;
> > +			}
> > +		} else {
> > +			spin_lock_irqsave(&zone->lock, flags);
> > +		}
> 
> [Severity: Medium]
> In show_free_areas(), when can_spin_trylock() returns false (such as in NMI or
> hardirq context under CONFIG_PREEMPT_RT, or in NMI context under !CONFIG_SMP):
> 
> mm/internal.h:can_spin_trylock() {
> 	if (IS_ENABLED(CONFIG_PREEMPT_RT) && (in_nmi() || in_hardirq()))
> 		return false;
> 
> 	/* On UP, spin_trylock() always succeeds even when it is locked */
> 	if (!IS_ENABLED(CONFIG_SMP) && in_nmi())
> 		return false;
> 
> 	return true;
> }
> 
> the inner !can_spin_trylock() check short-circuits before
> spin_trylock_irqsave() is ever called, yet still prints "zone %s lock
> contended" for every populated zone even when zone->lock is completely
> uncontended.
> 
> The commit message also states:
> 
>   Check can_spin_trylock() and use spin_trylock_irqsave() when
>   !can_spin_trylock(), in_nmi(), oops_in_progress, or panic_in_progress()
>   is active
> 
> Additionally, because show_node(zone) is moved after spin_unlock_irqrestore()
> below, skipping a zone here only logs zone->name (for example, Normal or
> DMA32) without the NUMA node ID on CONFIG_NUMA systems.
> 
> Should the !can_spin_trylock() case avoid claiming that zone->lock is
> contended (and match the commit message description), and should the skipped
> zone message include the node ID?
> 
> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/20261103024453.922373-1-atomlin@xxxxxxxxxxx?part=2

I have updated the commit message in the next revision to accurately
describe this two-stage check, and updated the pr_warn() message to include
the NUMA node ID via zone_to_nid(zone).

Kind regards,
-- 
Aaron Tomlin