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

Uladzislau Rezki
2023-05-24T09:15:13Z

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>

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Uladzislau Rezki