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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pAG2X-008GpV-Bv; Tue, 27 Dec 2022 19:55:09 +0000 Date: Tue, 27 Dec 2022 19:55:09 +0000 From: Matthew Wilcox To: SeongJae Park Cc: akpm@linux-foundation.org, alexander.h.duyck@linux.intel.com, paulmck@kernel.org, linux-mm@kvack.org, rcu@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/page_reporting: replace rcu_access_pointer() with rcu_dereference_protected() Message-ID: References: <20221227192158.2553-1-sj@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221227192158.2553-1-sj@kernel.org> X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: C4E334000C X-Rspam-User: X-Stat-Signature: d544b1r7hagg3ggwo8uy94qsacdqtcqs X-HE-Tag: 1672170906-850601 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Dec 27, 2022 at 07:21:58PM +0000, SeongJae Park wrote: > +++ b/mm/page_reporting.c > @@ -356,7 +356,7 @@ int page_reporting_register(struct page_reporting_dev_info *prdev) > mutex_lock(&page_reporting_mutex); > > /* nothing to do if already in use */ > - if (rcu_access_pointer(pr_dev_info)) { > + if (rcu_dereference_protected(pr_dev_info, true)) { Pretty sure that passing a bare 'true' is an antipattern. Instead, document _what_ lock protects us, ie: if (rcu_dereference_protected(pr_dev_info, lockdep_is_held(&page_reporting_mutex))) { Obviously, we took it just one line up, but if code moves around, it may save us.