Re: [PATCH 2/2] mm/page_alloc: don't spin_trylock() when disallowed in free_one_page()

[Vlastimil Babka (SUSE)]

On 7/15/26 11:03, Brendan Jackman wrote:
> __free_frozen_pages() checks can_spin_trylock() before entering into the
> main free_frozen_page_commit()/free_one_page() path, but before this it
> can get to free_one_page() via the !pcp_allowed_order() and
> MIGRATE_ISOLATE paths.
> 
> The !pcp_allowed_order() path depends on usage by callers so might not
> be possible in practice. The MIGRATE_ISOLATE path probably means kernel
> crashes and privilege escalation if anyone ever did memory hotplug and
> BPF tracing on a PREEMPT_RT or !SMP build.
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 8c57b687e8331 ("mm, bpf: Introduce free_pages_nolock()")
> Reported-by: sashiko-bot@xxxxxxxxxx
> Link: https://sashiko.dev/#/patchset/20260710-spin-trylock-followup-v1-0-affb5fe5ed00%40google.com?part=2

Closes: also

> Signed-off-by: Brendan Jackman <jackmanb@xxxxxxxxxx>

Reviewed-by: Vlastimil Babka (SUSE) <vbabka@xxxxxxxxxx>

> ---
>  mm/page_alloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 5f9873dfccc5a..46e5ea59c71df 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1559,7 +1559,7 @@ static void free_one_page(struct zone *zone, struct page *page,
>  	unsigned long flags;
>  
>  	if (unlikely(fpi_flags & FPI_TRYLOCK)) {
> -		if (!spin_trylock_irqsave(&zone->lock, flags)) {
> +		if (!can_spin_trylock() || !spin_trylock_irqsave(&zone->lock, flags)) {
>  			add_page_to_zone_llist(zone, page, order);
>  			return;
>  		}
>