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

[Zhaoyang Huang <huangzhaoyang@gmail.com>]

On Thu, Jun 6, 2024 at 10:42 AM Baoquan He <bhe@redhat.com> wrote:
>
> 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?
The vbq access will be totally mixed by your suggestion which means
vb_alloc on CPUx could get the vb on every CPU which has per_cpu
declaration making no sense.

>
> >
> > On Tue, Jun 4, 2024 at 10:23 AM zhaoyang.huang
> > <zhaoyang.huang@unisoc.com> wrote:
> > >
> > > From: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
> > >
> > > 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@oppo.com/
> > >
> > > Suggested-by: Hailong.Liu <hailong.liu@oppo.com>
> > > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
> > > ---
> > > 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
> > >
> >
>