linux-kernel - Re: [PATCH] mm: fix incorrect vbq reference in purge_fragmented

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Date: Thu, 30 May 2024 17:16:16 +0800
From: Chuanhua Han <chuanhuahan@...il.com>
To: "zhaoyang.huang" <zhaoyang.huang@...soc.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Uladzislau Rezki <urezki@...il.com>, 
	Christoph Hellwig <hch@...radead.org>, Lorenzo Stoakes <lstoakes@...il.com>, Baoquan He <bhe@...hat.com>, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	Zhaoyang Huang <huangzhaoyang@...il.com>, steve.kang@...soc.com
Subject: Re: [PATCH] mm: fix incorrect vbq reference in purge_fragmented_block

zhaoyang.huang <zhaoyang.huang@...soc.com> 于2024年5月30日周四 10:52写道：
>
> From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
>
> Broken vbq->free reported on a v6.6 based system which is caused
> by invalid vbq->lock protect over vbq->free in purge_fragmented_block.
> This should be introduced by the Fixes below which ignored vbq->lock
> matter.
>
> Fixes: fc1e0d980037 ("mm/vmalloc: prevent stale TLBs in fully utilized blocks")
>
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> ---
>  mm/vmalloc.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 22aa63f4ef63..112b50431725 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2614,9 +2614,10 @@ static void free_vmap_block(struct vmap_block *vb)
>  }
>
>  static bool purge_fragmented_block(struct vmap_block *vb,
> -               struct vmap_block_queue *vbq, struct list_head *purge_list,
> -               bool force_purge)
> +               struct list_head *purge_list, bool force_purge)
>  {
> +       struct vmap_block_queue *vbq;
> +
>         if (vb->free + vb->dirty != VMAP_BBMAP_BITS ||
>             vb->dirty == VMAP_BBMAP_BITS)
>                 return false;
> @@ -2625,6 +2626,8 @@ static bool purge_fragmented_block(struct vmap_block *vb,
>         if (!(force_purge || vb->free < VMAP_PURGE_THRESHOLD))
>                 return false;
>
> +       vbq = container_of(addr_to_vb_xa(vb->va->va_start),
> +               struct vmap_block_queue, vmap_blocks);
This seems to be the same as before fix :),  the vbq found by
addr_to_vb_xa is still added to the xarray vbq, not necessarily to the
free_list vbq,
These two vbqs may not be the same, we need to find the vbq when added
to free_list.

For example:
We add vb to vbq1's xarray and vbq2's free_list, and we need to find
vbq2 instead of vbq1.
So I feel like this place isn't really fixed？
>         /* prevent further allocs after releasing lock */
>         WRITE_ONCE(vb->free, 0);
>         /* prevent purging it again */
> @@ -2664,7 +2667,7 @@ static void purge_fragmented_blocks(int cpu)
>                         continue;
>
>                 spin_lock(&vb->lock);
> -               purge_fragmented_block(vb, vbq, &purge, true);
> +               purge_fragmented_block(vb, &purge, true);
>                 spin_unlock(&vb->lock);
>         }
>         rcu_read_unlock();
> @@ -2801,7 +2804,7 @@ static void _vm_unmap_aliases(unsigned long start, unsigned long end, int flush)
>                          * not purgeable, check whether there is dirty
>                          * space to be flushed.
>                          */
> -                       if (!purge_fragmented_block(vb, vbq, &purge_list, false) &&
> +                       if (!purge_fragmented_block(vb, &purge_list, false) &&
>                             vb->dirty_max && vb->dirty != VMAP_BBMAP_BITS) {
>                                 unsigned long va_start = vb->va->va_start;
>                                 unsigned long s, e;
> --
> 2.25.1
>
>


-- 
Thanks,
Chuanhua