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References: <20240530025144.1570865-1-zhaoyang.huang@unisoc.com>
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From: Chuanhua Han <chuanhuahan@gmail.com>
Date: Thu, 30 May 2024 17:16:16 +0800
Message-ID: <CANzGp4+HJE_h+kBsx9cJzKxJRi3u_y204-numUgzYgJBo2AJfg@mail.gmail.com>
Subject: Re: [PATCH] mm: fix incorrect vbq reference in purge_fragmented_block
To: "zhaoyang.huang" <zhaoyang.huang@unisoc.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Uladzislau Rezki <urezki@gmail.com>, 
	Christoph Hellwig <hch@infradead.org>, Lorenzo Stoakes <lstoakes@gmail.com>, Baoquan He <bhe@redhat.com>, 
	linux-mm@kvack.org, linux-kernel@vger.kernel.org, 
	Zhaoyang Huang <huangzhaoyang@gmail.com>, steve.kang@unisoc.com
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zhaoyang.huang <zhaoyang.huang@unisoc.com> =E4=BA=8E2024=E5=B9=B45=E6=9C=88=
30=E6=97=A5=E5=91=A8=E5=9B=9B 10:52=E5=86=99=E9=81=93=EF=BC=9A
>
> From: Zhaoyang Huang <zhaoyang.huang@unisoc.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 bl=
ocks")
>
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@unisoc.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_lis=
t,
> -               bool force_purge)
> +               struct list_head *purge_list, bool force_purge)
>  {
> +       struct vmap_block_queue *vbq;
> +
>         if (vb->free + vb->dirty !=3D VMAP_BBMAP_BITS ||
>             vb->dirty =3D=3D VMAP_BBMAP_BITS)
>                 return false;
> @@ -2625,6 +2626,8 @@ static bool purge_fragmented_block(struct vmap_bloc=
k *vb,
>         if (!(force_purge || vb->free < VMAP_PURGE_THRESHOLD))
>                 return false;
>
> +       vbq =3D 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=EF=BC=9F
>         /* 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, fals=
e) &&
>                             vb->dirty_max && vb->dirty !=3D VMAP_BBMAP_BI=
TS) {
>                                 unsigned long va_start =3D vb->va->va_sta=
rt;
>                                 unsigned long s, e;
> --
> 2.25.1
>
>


--=20
Thanks,
Chuanhua