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([2602:ae:154a:9f01:d15:390f:de71:e264]) by smtp.gmail.com with ESMTPSA id ka14-20020a170903334e00b0019ccded6a46sm5090249plb.228.2023.03.05.11.36.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 05 Mar 2023 11:36:25 -0800 (PST) Message-ID: Date: Sun, 5 Mar 2023 11:36:22 -0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 Subject: Re: [PATCH 7/8] qemu-coroutine-lock: add smp_mb__after_rmw() Content-Language: en-US To: Paolo Bonzini , qemu-devel@nongnu.org Cc: gshan@redhat.com, eesposit@redhat.com, david@redhat.com, stefanha@redhat.com, cohuck@redhat.com, eauger@redhat.com References: <20230303171939.237819-1-pbonzini@redhat.com> <20230303171939.237819-8-pbonzini@redhat.com> From: Richard Henderson In-Reply-To: <20230303171939.237819-8-pbonzini@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::102b; envelope-from=richard.henderson@linaro.org; helo=mail-pj1-x102b.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 3/3/23 09:19, Paolo Bonzini wrote: > mutex->from_push and mutex->handoff in qemu-coroutine-lock implement > the familiar pattern: > > write a write b > smp_mb() smp_mb() > read b read a > > The memory barrier is required by the C memory model even after a > SEQ_CST read-modify-write operation such as QSLIST_INSERT_HEAD_ATOMIC. > Add it and avoid the unclear qatomic_mb_read() operation. > > Signed-off-by: Paolo Bonzini > --- > util/qemu-coroutine-lock.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) Reviewed-by: Richard Henderson r~