On Thu, Jun 13, 2024 at 04:41:34PM +0800, Baoquan He wrote:
> On 06/12/24 at 01:27pm, Uladzislau Rezki wrote:
> > On Wed, Jun 12, 2024 at 10:00:14AM +0800, Zhaoyang Huang wrote:
> > > On Wed, Jun 12, 2024 at 2:16 AM Uladzislau Rezki <urezki@xxxxxxxxx> wrote:
> > > >
> > > > >
> > > > > 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.
> > > > >
> > > > I have just returned from vacation. Give me some time to review your
> > > > patch. Meanwhile, do you have a reproducer? So i would like to see how
> > > > i can trigger an issue that is in question.
> > > This bug arises from an system wide android test which has been
> > > reported by many vendors. Keep mount/unmount an erofs partition is
> > > supposed to be a simple reproducer. IMO, the logic defect is obvious
> > > enough to be found by code review.
> > >
> > Baoquan, any objection about this v4?
> >
> > Your proposal about inserting a new vmap-block based on it belongs
> > to, i.e. not per-this-cpu, should fix an issue. The problem is that
> > such way does __not__ pre-load a current CPU what is not good.
>
> With my understand, when we start handling to insert vb to vbq->xa and
> vbq->free, the vmap_area allocation has been done, it doesn't impact the
> CPU preloading when adding it into which CPU's vbq->free, does it?
>
> Not sure if I miss anything about the CPU preloading.
>
Like explained below in this email-thread:
vb_alloc() inserts a new block _not_ on this CPU. This CPU tries to
allocate one more time and its free_list is empty(because on a prev.
step a block has been inserted into another CPU-block-queue), thus
it allocates a new block one more time and which is inserted most
likely on a next zone/CPU. And so on.
See:
<snip vb_alloc>
...
rcu_read_lock();
vbq = raw_cpu_ptr(&vmap_block_queue); <- Here it is correctly accessing this CPU
list_for_each_entry_rcu(vb, &vbq->free, free_list) {
unsigned long pages_off;
...
<snip vb_alloc>
<snip new_vmap_block>
...
vbq = addr_to_vbq(va->va_start); <- Here we insert based on hashing, i.e. not to this CPU-block-queue
spin_lock(&vbq->lock);
list_add_tail_rcu(&vb->free_list, &vbq->free);
spin_unlock(&vbq->lock);
...
<snip new_vmap_block>
Thanks!
--
Uladzislau Rezki
