Re: [PATCH mm] mm: fix BUG with kvzalloc+GFP_ATOMIC

[Michal Hocko]

On Mon 26-09-22 12:08:00, Florian Westphal wrote:
> Michal Hocko <mhocko@xxxxxxxx> wrote:
> > +		old_tbl = rht_dereference_rcu(ht->tbl, ht);
> > +		size = tbl->size;
> > +
> > +		data = ERR_PTR(-EBUSY);
> > +
> > +		if (rht_grow_above_75(ht, tbl))
> > +			size *= 2;
> > +		/* Do not schedule more than one rehash */
> > +		else if (old_tbl != tbl)
> > +			return data;
> > +
> > +		data = ERR_PTR(-ENOMEM);
> > +
> > +		rcu_read_unlock();
> > +		new_tbl = bucket_table_alloc(ht, size, GFP_KERNEL);
> > +		rcu_read_lock();
> 
> I don't think this is going to work, there can be callers that
> rely on rcu protected data structures getting free'd.

The caller of this function drops RCU for each retry, why should be the
called function any special?
-- 
Michal Hocko
SUSE Labs