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

[Zhaoyang Huang <huangzhaoyang@gmail.com>]

Sorry to bother you again. Are there any other comments or new patch
on this which block some test cases of ANDROID that only accept ACKed
one on its tree.

On Fri, Jun 7, 2024 at 4:30 PM Zhaoyang Huang <huangzhaoyang@gmail.com> wrote:
>
> Patchv4 was updated based on Hailong and Uladzislau's comments, where
> vbq is obtained from vb->cpu, thus avoiding disabling preemption.
> Furthermore, Baoquan's suggestion was not adopted because it made vbq
> accesses completely interleaved across all CPUs, which defeats the
> goal of per_cpu.
>
> On Fri, Jun 7, 2024 at 10:31 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
> >