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([38.41.223.211]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-22c33faac7asm17797435ad.137.2025.04.16.11.52.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 16 Apr 2025 11:52:24 -0700 (PDT) From: Pierrick Bouvier To: qemu-devel@nongnu.org Cc: philmd@linaro.org, Phil Dennis-Jordan , Paolo Bonzini , Nicholas Piggin , Stefan Hajnoczi , Pierrick Bouvier Subject: [PATCH] system/main: comment lock rationale Date: Wed, 16 Apr 2025 11:52:18 -0700 Message-Id: <20250416185218.1654157-1-pierrick.bouvier@linaro.org> X-Mailer: git-send-email 2.39.5 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2607:f8b0:4864:20::634; envelope-from=pierrick.bouvier@linaro.org; helo=mail-pl1-x634.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, 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 Signed-off-by: Pierrick Bouvier --- system/main.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/system/main.c b/system/main.c index 1c022067349..b8f7157cc34 100644 --- a/system/main.c +++ b/system/main.c @@ -69,8 +69,21 @@ int (*qemu_main)(void) = os_darwin_cfrunloop_main; int main(int argc, char **argv) { qemu_init(argc, argv); + + /* + * qemu_init acquires the BQL and replay mutex lock. BQL is acquired when + * initializing cpus, to block associated threads until initialization is + * complete. Replay_mutex lock is acquired on initialization, because it + * must be held when configuring icount_mode. + * + * On MacOS, qemu main event loop runs in a background thread, as main + * thread must be reserved for UI. Thus, we need to transfer lock ownership, + * and the simplest way to do that is to release them, and reacquire them + * from qemu_default_main. + */ bql_unlock(); replay_mutex_unlock(); + if (qemu_main) { QemuThread main_loop_thread; qemu_thread_create(&main_loop_thread, "qemu_main", -- 2.39.5