linux-kernel - Re: [PATCH 2/2] mm/slab: break up RCU readers on SLAB_TYPESAFE_BY

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Message-Id: <20230415032305.3860-1-sj@kernel.org>
Date:   Sat, 15 Apr 2023 03:23:05 +0000
From:   SeongJae Park <sj@...nel.org>
To:     "Paul E . McKenney" <paulmck@...nel.org>
Cc:     SeongJae Park <sj@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        akpm@...ux-foundation.org, vbabka@...e.cz, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm/slab: break up RCU readers on SLAB_TYPESAFE_BY_RCU example code

On Sat, 15 Apr 2023 03:04:52 +0000 SeongJae Park <sj@...nel.org> wrote:

> On Sat, 15 Apr 2023 03:51:54 +0100 Matthew Wilcox <willy@...radead.org> wrote:
> 
> > On Sat, Apr 15, 2023 at 12:37:53AM +0000, SeongJae Park wrote:
> > >   *
> > > + * begin:
> > >   *  rcu_read_lock();
> > > - * again:
> > >   *  obj = lockless_lookup(key);
> > >   *  if (obj) {
> > >   *    if (!try_get_ref(obj)) // might fail for free objects
> > > - *      goto again;
> > > + *      goto begin;

I simply followed the commit da82af04352b ("doc: Update and wordsmith
rculist_nulls.rst") for this change, and I think I overlooked this part.  If
I'm not missing something, I think we should call rcu_read_unlock() here too,
just before 'goto begin'.

I will post another patch for rculist_null.rst later.


Thanks,
SJ

> > >   *
> > >   *    if (obj->key != key) { // not the object we expected
> > >   *      put_ref(obj);
> > > + *      rcu_read_unlock();
> > >   *      goto again;
> > 
> > - *      goto again;
> > + *      goto begin;
> 
> Oops, thank you for catching, Matthew!
> 
> 
> Thanks,
> SJ