Re: [patch 5/6] mm/vmalloc: Add missing READ/WRITE_ONCE() annotations

[Uladzislau Rezki <urezki@gmail.com>]

On Tue, May 23, 2023 at 04:02:15PM +0200, Thomas Gleixner wrote:
> purge_fragmented_blocks() accesses vmap_block::free and vmap_block::dirty
> lockless for a quick check.
> 
> Add the missing READ/WRITE_ONCE() annotations.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  mm/vmalloc.c |   11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2093,9 +2093,9 @@ static bool purge_fragmented_block(struc
>  		return false;
>  
>  	 /* prevent further allocs after releasing lock */
> -	vb->free = 0;
> +	WRITE_ONCE(vb->free, 0);
>  	 /* prevent purging it again */
> -	vb->dirty = VMAP_BBMAP_BITS;
> +	WRITE_ONCE(vb->dirty, VMAP_BBMAP_BITS);
>  	vb->dirty_min = 0;
>  	vb->dirty_max = VMAP_BBMAP_BITS;
>  	spin_lock(&vbq->lock);
> @@ -2123,7 +2123,10 @@ static void purge_fragmented_blocks(int
>  
>  	rcu_read_lock();
>  	list_for_each_entry_rcu(vb, &vbq->free, free_list) {
> -		if (!(vb->free + vb->dirty == VMAP_BBMAP_BITS && vb->dirty != VMAP_BBMAP_BITS))
> +		unsigned long free = READ_ONCE(vb->free);
> +		unsigned long dirty = READ_ONCE(vb->dirty);
> +
> +		if (!(free + dirty == VMAP_BBMAP_BITS && dirty != VMAP_BBMAP_BITS))
>  			continue;
>  
>  		spin_lock(&vb->lock);
> @@ -2231,7 +2234,7 @@ static void vb_free(unsigned long addr,
>  	vb->dirty_min = min(vb->dirty_min, offset);
>  	vb->dirty_max = max(vb->dirty_max, offset + (1UL << order));
>  
> -	vb->dirty += 1UL << order;
> +	WRITE_ONCE(vb->dirty, vb->dirty + (1UL << order));
>  	if (vb->dirty == VMAP_BBMAP_BITS) {
>  		BUG_ON(vb->free);
>  		spin_unlock(&vb->lock);
> 
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>

--
Uladzislau Rezki