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[46.135.86.144]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5e5c7476ab2sm8746169a12.31.2025.03.11.08.44.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 11 Mar 2025 08:44:48 -0700 (PDT) Date: Tue, 11 Mar 2025 16:44:30 +0100 From: Mateusz Guzik To: Alexei Starovoitov Cc: bpf@vger.kernel.org, andrii@kernel.org, memxor@gmail.com, akpm@linux-foundation.org, peterz@infradead.org, vbabka@suse.cz, bigeasy@linutronix.de, rostedt@goodmis.org, houtao1@huawei.com, hannes@cmpxchg.org, shakeel.butt@linux.dev, mhocko@suse.com, willy@infradead.org, tglx@linutronix.de, jannh@google.com, tj@kernel.org, linux-mm@kvack.org, kernel-team@fb.com Subject: Re: [PATCH bpf-next v9 1/6] locking/local_lock: Introduce localtry_lock_t Message-ID: References: <20250222024427.30294-1-alexei.starovoitov@gmail.com> <20250222024427.30294-2-alexei.starovoitov@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20250222024427.30294-2-alexei.starovoitov@gmail.com> X-Rspam-User: X-Rspamd-Queue-Id: 84C14A0027 X-Stat-Signature: ys6ynhhyi4skb8mgseggd8m5j6o4uim3 X-Rspamd-Server: rspam10 X-HE-Tag: 1741707891-196375 X-HE-Meta: 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 WVjImI8g 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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: List-Subscribe: List-Unsubscribe: On Fri, Feb 21, 2025 at 06:44:22PM -0800, Alexei Starovoitov wrote: > +#define __localtry_lock(lock) \ > + do { \ > + localtry_lock_t *lt; \ > + preempt_disable(); \ > + lt = this_cpu_ptr(lock); \ > + local_lock_acquire(<->llock); \ > + WRITE_ONCE(lt->acquired, 1); \ > + } while (0) I think these need compiler barriers. I checked with gcc docs (https://gcc.gnu.org/onlinedocs/gcc/Volatiles.html) and found this as confirmation: > Accesses to non-volatile objects are not ordered with respect to volatile accesses. Unless the Linux kernel is built with some magic to render this moot(?).