From patchwork Wed Oct 19 22:46:56 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Paul E. McKenney" X-Patchwork-Id: 13012450 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id F2852C4332F for ; Wed, 19 Oct 2022 22:47:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230393AbiJSWrJ (ORCPT ); Wed, 19 Oct 2022 18:47:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36114 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230299AbiJSWrE (ORCPT ); Wed, 19 Oct 2022 18:47:04 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B463E186D70; Wed, 19 Oct 2022 15:47:03 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 64496B825E1; Wed, 19 Oct 2022 22:47:02 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0562DC4347C; Wed, 19 Oct 2022 22:47:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1666219621; bh=U+1luf3mbgyTSKOMl8vtX4dFmH8rl+GKNY2TDjN1IyY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=XMSKFGEu/uzR3N52gimUSRvlUY77ksX6bwSP5MEEbrhoYubbKoJVO455NMN69R4xj x9GRwiRrinWyIWvqcLaI+JhV5ZHw0Ow+vjol3spPlLV+EDFsRspfhySJYB1hNYEyDD aSGLKC8qpWBT4nbxwHNQOo7RmG1Z0Y+5PDZjmaBTcnkG3j3YRGb2Ycr+/iXr0GVAM8 f3R8P+eO4JCLRSgp7mHQtfS9keccHmF/hGloP0UzUPKujvCNZbkgV3dyp0o5SzcWdJ GLdFjAAokYxUviKsgseded/9rmE6dJI2yUYwAvyjELLvaU6fXnXMYEQiD9ItgNieST uSvkQeYinB1kw== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id AD5D05C0A04; Wed, 19 Oct 2022 15:47:00 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, rostedt@goodmis.org, "Paul E. McKenney" , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Vlastimil Babka , Roman Gushchin , Hyeonggon Yoo <42.hyeyoo@gmail.com>, linux-mm@kvack.org Subject: [PATCH rcu 5/8] slab: Explain why SLAB_DESTROY_BY_RCU reference before locking Date: Wed, 19 Oct 2022 15:46:56 -0700 Message-Id: <20221019224659.2499511-5-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20221019224652.GA2499358@paulmck-ThinkPad-P17-Gen-1> References: <20221019224652.GA2499358@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org It is not obvious to the casual user why it is absolutely necessary to acquire a reference to a SLAB_DESTROY_BY_RCU structure before acquiring a lock in that structure. Therefore, add a comment explaining this point. Signed-off-by: Paul E. McKenney Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Cc: Andrew Morton Cc: Vlastimil Babka Cc: Roman Gushchin Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com> Cc: Acked-by: Vlastimil Babka --- include/linux/slab.h | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/include/linux/slab.h b/include/linux/slab.h index 90877fcde70bd..446303e385265 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -76,6 +76,12 @@ * rcu_read_lock before reading the address, then rcu_read_unlock after * taking the spinlock within the structure expected at that address. * + * Note that it is not possible to acquire a lock within a structure + * allocated with SLAB_DESTROY_BY_RCU without first acquiring a reference + * as described above. The reason is that SLAB_DESTROY_BY_RCU pages are + * not zeroed before being given to the slab, which means that any locks + * must be initialized after each and every kmem_struct_alloc(). + * * Note that SLAB_TYPESAFE_BY_RCU was originally named SLAB_DESTROY_BY_RCU. */ /* Defer freeing slabs to RCU */