Re: [PATCHv4 1/1] mm: fix incorrect vbq reference in purge_fragmented_block

[Baoquan He]

On 06/06/24 at 10:28am, Zhaoyang Huang wrote:
> This patch is urgent for the Android world which uses v6.6 now. Is
> there any comments on this? Thanks!

You should take the way Willf and I suggested, to adjust the vba->free
to only contain the vb belonging to it. Have you tested the draft patch?

> 
> On Tue, Jun 4, 2024 at 10:23 AM zhaoyang.huang
> <zhaoyang.huang@xxxxxxxxxx> wrote:
> >
> > From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> >
> > vmalloc area runs out in our ARM64 system during an erofs test as
> > vm_map_ram failed[1]. By following the debug log, we find that
> > vm_map_ram()->vb_alloc() will allocate new vb->va which corresponding
> > to 4MB vmalloc area as list_for_each_entry_rcu returns immediately
> > when vbq->free->next points to vbq->free. That is to say, 65536 times
> > of page fault after the list's broken will run out of the whole
> > vmalloc area. This should be introduced by one vbq->free->next point to
> > vbq->free which makes list_for_each_entry_rcu can not iterate the list
> > and find the BUG.
> >
> > [1]
> > PID: 1        TASK: ffffff80802b4e00  CPU: 6    COMMAND: "init"
> >  #0 [ffffffc08006afe0] __switch_to at ffffffc08111d5cc
> >  #1 [ffffffc08006b040] __schedule at ffffffc08111dde0
> >  #2 [ffffffc08006b0a0] schedule at ffffffc08111e294
> >  #3 [ffffffc08006b0d0] schedule_preempt_disabled at ffffffc08111e3f0
> >  #4 [ffffffc08006b140] __mutex_lock at ffffffc08112068c
> >  #5 [ffffffc08006b180] __mutex_lock_slowpath at ffffffc08111f8f8
> >  #6 [ffffffc08006b1a0] mutex_lock at ffffffc08111f834
> >  #7 [ffffffc08006b1d0] reclaim_and_purge_vmap_areas at ffffffc0803ebc3c
> >  #8 [ffffffc08006b290] alloc_vmap_area at ffffffc0803e83fc
> >  #9 [ffffffc08006b300] vm_map_ram at ffffffc0803e78c0
> >
> > Fixes: fc1e0d980037 ("mm/vmalloc: prevent stale TLBs in fully utilized blocks")
> >
> > For detailed reason of broken list, please refer to below URL
> > https://lore.kernel.org/all/20240531024820.5507-1-hailong.liu@xxxxxxxx/
> >
> > Suggested-by: Hailong.Liu <hailong.liu@xxxxxxxx>
> > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> > ---
> > v2: introduce cpu in vmap_block to record the right CPU number
> > v3: use get_cpu/put_cpu to prevent schedule between core
> > v4: replace get_cpu/put_cpu by another API to avoid disabling preemption
> > ---
> > ---
> >  mm/vmalloc.c | 21 +++++++++++++++------
> >  1 file changed, 15 insertions(+), 6 deletions(-)
> >
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index 22aa63f4ef63..89eb034f4ac6 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -2458,6 +2458,7 @@ struct vmap_block {
> >         struct list_head free_list;
> >         struct rcu_head rcu_head;
> >         struct list_head purge;
> > +       unsigned int cpu;
> >  };
> >
> >  /* Queue of free and dirty vmap blocks, for allocation and flushing purposes */
> > @@ -2585,8 +2586,15 @@ static void *new_vmap_block(unsigned int order, gfp_t gfp_mask)
> >                 free_vmap_area(va);
> >                 return ERR_PTR(err);
> >         }
> > -
> > -       vbq = raw_cpu_ptr(&vmap_block_queue);
> > +       /*
> > +        * list_add_tail_rcu could happened in another core
> > +        * rather than vb->cpu due to task migration, which
> > +        * is safe as list_add_tail_rcu will ensure the list's
> > +        * integrity together with list_for_each_rcu from read
> > +        * side.
> > +        */
> > +       vb->cpu = raw_smp_processor_id();
> > +       vbq = per_cpu_ptr(&vmap_block_queue, vb->cpu);
> >         spin_lock(&vbq->lock);
> >         list_add_tail_rcu(&vb->free_list, &vbq->free);
> >         spin_unlock(&vbq->lock);
> > @@ -2614,9 +2622,10 @@ 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 = &per_cpu(vmap_block_queue, vb->cpu);
> > +
> >         if (vb->free + vb->dirty != VMAP_BBMAP_BITS ||
> >             vb->dirty == VMAP_BBMAP_BITS)
> >                 return false;
> > @@ -2664,7 +2673,7 @@ 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 +2810,7 @@ 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
> >
>