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Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98 #2 (Red Hat Linux)) id 1tERgv-00000007adG-46gR; Fri, 22 Nov 2024 11:19:15 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 479EA30066A; Fri, 22 Nov 2024 12:19:14 +0100 (CET) Date: Fri, 22 Nov 2024 12:19:14 +0100 From: Peter Zijlstra To: David Hildenbrand Cc: Suren Baghdasaryan , akpm@linux-foundation.org, andrii@kernel.org, jannh@google.com, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, vbabka@suse.cz, mhocko@kernel.org, shakeel.butt@linux.dev, hannes@cmpxchg.org, willy@infradead.org, brauner@kernel.org, oleg@redhat.com, arnd@arndb.de, richard.weiyang@gmail.com, zhangpeng.00@bytedance.com, linmiaohe@huawei.com, viro@zeniv.linux.org.uk, hca@linux.ibm.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/3] seqlock: add raw_seqcount_try_begin Message-ID: <20241122111914.GS24774@noisy.programming.kicks-ass.net> References: <20241121162826.987947-1-surenb@google.com> <46aa36f0-64a6-4aee-8134-0ec93f62e59c@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <46aa36f0-64a6-4aee-8134-0ec93f62e59c@redhat.com> X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: E11DB4000A X-Stat-Signature: kfgq84o1bz3nme95879ecromonydb7wo X-Rspam-User: X-HE-Tag: 1732274325-159633 X-HE-Meta: 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 2fBRiYnt QuxfMtyKtBLvxLhyzXB+Urt6uNv+dpoCMw0yYRlobYIrLlDzzlNLeLgRHM0Y02EEB+rC3xTDIZz9jxDKV280fzq4Z66IroJkdpFWIMVjdD4pXcLI9Fg8JRZqn6SkAXvqcoWH2ggx0LJKIfH3zi4juSyng4ZWMH3PblRGR1tm2lE6Yjipyxl+bVyBY8rQGT0yJE8jve2OkPalrVzk+4+DqJuzJoq3Lcjhs5RlqdnZ0lkCPRjjqV+7q9bifBfyEiuIAOa6PwdnooDhdgMWMVbjDOUrB951zPMzrtDagVXxYzRqOtccLvLOScnLdKg== 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: List-Subscribe: List-Unsubscribe: On Fri, Nov 22, 2024 at 12:10:29PM +0100, David Hildenbrand wrote: > In gup_fast(), we simply do > > seq = raw_read_seqcount(¤t->mm->write_protect_seq); > if (seq & 1) > return 0; > > Should we be using that there as well? > > if (!raw_seqcount_try_begin(¤t->mm->write_protect_seqs, seq)) > return 0; Might as well. A quick grep doesn't find me another instance of this pattern, but does find me something 'funny' in net/netfilter/x_tables.c. Let's pretend I didn't see that for now ... *sigh* Want me to stick a patch like this on, or do you want to do that later, when the dust has settled?