From: Joel Fernandes <joel@joelfernandes.org>
To: SeongJae Park <sj@kernel.org>
Cc: paulmck@kernel.org, corbet@lwn.net, rcu@vger.kernel.org,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/4] Docs/RCU/rculist_nulls: Drop unnecessary '_release' in insert function
Date: Fri, 19 May 2023 14:52:50 -0400 [thread overview]
Message-ID: <CAEXW_YQFqW2QcAuHZEhc_GaUaB-=QOS0WgUOizd=FYwtFQ8vag@mail.gmail.com> (raw)
In-Reply-To: <20230518224008.2468-5-sj@kernel.org>
On Thu, May 18, 2023 at 6:40 PM SeongJae Park <sj@kernel.org> wrote:
>
> The document says we can avoid extra smp_rmb() in lockless_lookup() and
> extra _release() in insert function when hlist_nulls is used. However,
> the example code snippet for the insert function is still using the
> extra _release(). Drop it.
>
> Signed-off-by: SeongJae Park <sj@kernel.org>
> ---
> Documentation/RCU/rculist_nulls.rst | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/Documentation/RCU/rculist_nulls.rst b/Documentation/RCU/rculist_nulls.rst
> index 5cd6f3f8810f..463270273d89 100644
> --- a/Documentation/RCU/rculist_nulls.rst
> +++ b/Documentation/RCU/rculist_nulls.rst
> @@ -191,7 +191,7 @@ scan the list again without harm.
> obj = kmem_cache_alloc(cachep);
> lock_chain(); // typically a spin_lock()
> obj->key = key;
> - atomic_set_release(&obj->refcnt, 1); // key before refcnt
> + atomic_set(&obj->refcnt, 1);
> /*
> * insert obj in RCU way (readers might be traversing chain)
> */
If write to ->refcnt of 1 is reordered with setting of ->key, what
prevents the 'lookup algorithm' from doing a key match (obj->key ==
key) before the refcount has been initialized?
Are we sure the reordering mentioned in the document is the same as
the reordering prevented by the atomic_set_release()?
For the other 3 patches, feel free to add:
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
thanks,
- Joel
next prev parent reply other threads:[~2023-05-19 18:53 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-18 22:40 [PATCH 0/4] Docs/RCU/rculist_nulls: Minor fixups SeongJae Park
2023-05-18 22:40 ` [PATCH 1/4] Docs/RCU/rculist_nulls: Fix trivial coding style SeongJae Park
2023-05-18 22:40 ` [PATCH 2/4] Docs/RCU/rculist_nulls: Assign 'obj' before use from the examples SeongJae Park
2023-05-18 22:40 ` [PATCH 3/4] Docs/RCU/rculist_nulls: Fix hlist_head field name of 'obj' SeongJae Park
2023-05-18 22:40 ` [PATCH 4/4] Docs/RCU/rculist_nulls: Drop unnecessary '_release' in insert function SeongJae Park
2023-05-19 18:52 ` Joel Fernandes [this message]
2023-06-09 19:12 ` SeongJae Park
2023-06-09 23:42 ` Paul E. McKenney
2023-06-10 0:20 ` SeongJae Park
2023-06-10 5:52 ` Alan Huang
2023-06-10 5:37 ` Alan Huang
2023-06-10 11:04 ` Alan Huang
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