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

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Date: Thu, 30 May 2024 17:25:30 +0800
From: Zhaoyang Huang <huangzhaoyang@...il.com>
To: Chuanhua Han <chuanhuahan@...il.com>
Cc: "zhaoyang.huang" <zhaoyang.huang@...soc.com>, 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, steve.kang@...soc.com
Subject: Re: [PATCH] mm: fix incorrect vbq reference in purge_fragmented_block

On Thu, May 30, 2024 at 5:16 PM Chuanhua Han <chuanhuahan@...il.com> wrote:
>
> 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,
Yes, my fault. Should we expand the vmap_block_queue by introducing a
cpu_id which I actually do in my local regression.

> 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