On 12/11/18 11:45 AM, Matthew Wilcox wrote:
> On Tue, Dec 11, 2018 at 11:41:55AM -0700, Jens Axboe wrote:
>> On Wed, Nov 28, 2018 at 11:35 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>>>
>>> rcu_read_lock();
>>> - table = rcu_dereference(mm->ioctx_table);
>>> -
>>> - if (!table || id >= table->nr)
>>> - goto out;
>>> -
>>> - ctx = rcu_dereference(table->table[id]);
>>> + ctx = xa_load(&mm->ioctx, id);
>>> if (ctx && ctx->user_id == ctx_id) {
>>> if (percpu_ref_tryget_live(&ctx->users))
>>> ret = ctx;
>>> }
>>
>> Question on this part - do we need that RCU read lock around this now? I
>> don't think we do.
>
> I think we need the rcu read lock here to prevent ctx from being freed
> under us by free_ioctx().
Then that begs the question, how about __xa_load() that is already called
under RCU read lock?
--
Jens Axboe
