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Tue, 10 Jan 2023 09:46:58 -0800 (PST) Received: from zen.lan (localhost [127.0.0.1]) by zen.linaroharston (Postfix) with ESMTP id A9AAC1FFCC; Tue, 10 Jan 2023 17:39:25 +0000 (GMT) From: =?utf-8?q?Alex_Benn=C3=A9e?= To: qemu-devel@nongnu.org Cc: Richard Henderson , Alexandre Iooss , Beraldo Leal , Thomas Huth , John Snow , Eduardo Habkost , Elena Ufimtseva , Ed Maste , Yanan Wang , Cleber Rosa , =?utf-8?q?Marc-Andr=C3=A9_Lureau?= , Li-Wen Hsu , Markus Armbruster , Jagannathan Raman , =?utf-8?q?Daniel_P=2E_Berrang?= =?utf-8?q?=C3=A9?= , =?utf-8?q?Philippe_Mathieu-Daud?= =?utf-8?q?=C3=A9?= , Michael Roth , Wainer dos Santos Moschetta , =?utf-8?q?Alex_Benn?= =?utf-8?q?=C3=A9e?= , qemu-arm@nongnu.org, Marcel Apfelbaum , Peter Maydell , Paolo Bonzini , Mahmoud Mandour , John G Johnson , Emilio Cota Subject: [PATCH 22/26] plugins: make qemu_plugin_user_exit's locking order consistent with fork_start's Date: Tue, 10 Jan 2023 17:39:18 +0000 Message-Id: <20230110173922.265055-23-alex.bennee@linaro.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230110173922.265055-1-alex.bennee@linaro.org> References: <20230110173922.265055-1-alex.bennee@linaro.org> MIME-Version: 1.0 Received-SPF: pass client-ip=2a00:1450:4864:20::334; envelope-from=alex.bennee@linaro.org; helo=mail-wm1-x334.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+patch=linaro.org@nongnu.org Sender: qemu-devel-bounces+patch=linaro.org@nongnu.org From: Emilio Cota To fix potential deadlocks as reported by tsan. Reviewed-by: Richard Henderson Signed-off-by: Emilio Cota Reviewed-by: Philippe Mathieu-Daudé Message-Id: <20230109224954.161672-6-cota@braap.org> Signed-off-by: Alex Bennée --- plugins/core.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) diff --git a/plugins/core.c b/plugins/core.c index ccb770a485..728bacef95 100644 --- a/plugins/core.c +++ b/plugins/core.c @@ -500,10 +500,17 @@ void qemu_plugin_user_exit(void) enum qemu_plugin_event ev; CPUState *cpu; - QEMU_LOCK_GUARD(&plugin.lock); - + /* + * Locking order: we must acquire locks in an order that is consistent + * with the one in fork_start(). That is: + * - start_exclusive(), which acquires qemu_cpu_list_lock, + * must be called before acquiring plugin.lock. + * - tb_flush(), which acquires mmap_lock(), must be called + * while plugin.lock is not held. + */ start_exclusive(); + qemu_rec_mutex_lock(&plugin.lock); /* un-register all callbacks except the final AT_EXIT one */ for (ev = 0; ev < QEMU_PLUGIN_EV_MAX; ev++) { if (ev != QEMU_PLUGIN_EV_ATEXIT) { @@ -513,13 +520,12 @@ void qemu_plugin_user_exit(void) } } } - - tb_flush(current_cpu); - CPU_FOREACH(cpu) { qemu_plugin_disable_mem_helpers(cpu); } + qemu_rec_mutex_unlock(&plugin.lock); + tb_flush(current_cpu); end_exclusive(); /* now it's safe to handle the exit case */