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Tue, 20 Jul 2021 16:44:19 -0700 (PDT) Received: from zen.linaroharston ([51.148.130.216]) by smtp.gmail.com with ESMTPSA id e11sm30953346wrt.0.2021.07.20.16.44.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Jul 2021 16:44:18 -0700 (PDT) Received: from zen.lan (localhost [127.0.0.1]) by zen.linaroharston (Postfix) with ESMTP id B01A91FFA9; Wed, 21 Jul 2021 00:27:05 +0100 (BST) From: =?utf-8?q?Alex_Benn=C3=A9e?= To: qemu-devel@nongnu.org Subject: [PATCH v1 20/29] tcg/plugins: implement a qemu_plugin_user_exit helper Date: Wed, 21 Jul 2021 00:26:54 +0100 Message-Id: <20210720232703.10650-21-alex.bennee@linaro.org> X-Mailer: git-send-email 2.32.0.264.g75ae10bc75 In-Reply-To: <20210720232703.10650-1-alex.bennee@linaro.org> References: <20210720232703.10650-1-alex.bennee@linaro.org> MIME-Version: 1.0 Received-SPF: pass client-ip=2a00:1450:4864:20::32a; envelope-from=alex.bennee@linaro.org; helo=mail-wm1-x32a.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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: fam@euphon.net, berrange@redhat.com, Kyle Evans , f4bug@amsat.org, Laurent Vivier , Warner Losh , stefanha@redhat.com, crosa@redhat.com, pbonzini@redhat.com, Mahmoud Mandour , Alexandre Iooss , =?utf-8?q?Alex_Benn=C3=A9e?= , aurelien@aurel32.net Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" In user-mode emulation there is a small race between preexit_cleanup and exit_group() which means we may end up calling instrumented instructions before the kernel reaps child threads. To solve this we implement a new helper which ensures the callbacks are flushed along with any translations before we let the host do it's a thing. While we are at it make the documentation of qemu_plugin_register_atexit_cb clearer as to what the user can expect. Signed-off-by: Alex Bennée Reviewed-by: Mahmoud Mandour Acked-by: Warner Losh Message-Id: <20210719123732.24457-1-alex.bennee@linaro.org> --- v2 - included qemu_plugin_disable_mem_helpers --- include/qemu/plugin.h | 12 ++++++++++++ include/qemu/qemu-plugin.h | 13 +++++++++++++ bsd-user/syscall.c | 6 +++--- linux-user/exit.c | 2 +- plugins/core.c | 39 ++++++++++++++++++++++++++++++++++++++ 5 files changed, 68 insertions(+), 4 deletions(-) diff --git a/include/qemu/plugin.h b/include/qemu/plugin.h index 0fefbc6084..9a8438f683 100644 --- a/include/qemu/plugin.h +++ b/include/qemu/plugin.h @@ -190,6 +190,16 @@ void qemu_plugin_add_dyn_cb_arr(GArray *arr); void qemu_plugin_disable_mem_helpers(CPUState *cpu); +/** + * qemu_plugin_user_exit(): clean-up callbacks before calling exit callbacks + * + * This is a user-mode only helper that ensure we have fully cleared + * callbacks from all threads before calling the exit callbacks. This + * is so the plugins themselves don't have to jump through hoops to + * guard against race conditions. + */ +void qemu_plugin_user_exit(void); + #else /* !CONFIG_PLUGIN */ static inline void qemu_plugin_add_opts(void) @@ -250,6 +260,8 @@ void qemu_plugin_add_dyn_cb_arr(GArray *arr) static inline void qemu_plugin_disable_mem_helpers(CPUState *cpu) { } +static inline void qemu_plugin_user_exit(void) +{ } #endif /* !CONFIG_PLUGIN */ #endif /* QEMU_PLUGIN_H */ diff --git a/include/qemu/qemu-plugin.h b/include/qemu/qemu-plugin.h index dc3496f36c..e6e815abc5 100644 --- a/include/qemu/qemu-plugin.h +++ b/include/qemu/qemu-plugin.h @@ -549,6 +549,19 @@ void qemu_plugin_vcpu_for_each(qemu_plugin_id_t id, void qemu_plugin_register_flush_cb(qemu_plugin_id_t id, qemu_plugin_simple_cb_t cb); +/** + * qemu_plugin_register_atexit_cb() - register exit callback + * @id: plugin ID + * @cb: callback + * @userdata: user data for callback + * + * The @cb function is called once execution has finished. Plugins + * should be able to free all their resources at this point much like + * after a reset/uninstall callback is called. + * + * In user-mode it is possible a few un-instrumented instructions from + * child threads may run before the host kernel reaps the threads. + */ void qemu_plugin_register_atexit_cb(qemu_plugin_id_t id, qemu_plugin_udata_cb_t cb, void *userdata); diff --git a/bsd-user/syscall.c b/bsd-user/syscall.c index 7d986e9700..3f44311396 100644 --- a/bsd-user/syscall.c +++ b/bsd-user/syscall.c @@ -335,7 +335,7 @@ abi_long do_freebsd_syscall(void *cpu_env, int num, abi_long arg1, _mcleanup(); #endif gdb_exit(arg1); - qemu_plugin_atexit_cb(); + qemu_plugin_user_exit(); /* XXX: should free thread stack and CPU env */ _exit(arg1); ret = 0; /* avoid warning */ @@ -437,7 +437,7 @@ abi_long do_netbsd_syscall(void *cpu_env, int num, abi_long arg1, _mcleanup(); #endif gdb_exit(arg1); - qemu_plugin_atexit_cb(); + qemu_plugin_user_exit(); /* XXX: should free thread stack and CPU env */ _exit(arg1); ret = 0; /* avoid warning */ @@ -516,7 +516,7 @@ abi_long do_openbsd_syscall(void *cpu_env, int num, abi_long arg1, _mcleanup(); #endif gdb_exit(arg1); - qemu_plugin_atexit_cb(); + qemu_plugin_user_exit(); /* XXX: should free thread stack and CPU env */ _exit(arg1); ret = 0; /* avoid warning */ diff --git a/linux-user/exit.c b/linux-user/exit.c index 70b344048c..527e29cbc1 100644 --- a/linux-user/exit.c +++ b/linux-user/exit.c @@ -35,5 +35,5 @@ void preexit_cleanup(CPUArchState *env, int code) __gcov_dump(); #endif gdb_exit(code); - qemu_plugin_atexit_cb(); + qemu_plugin_user_exit(); } diff --git a/plugins/core.c b/plugins/core.c index e1bcdb570d..7cf4f87e18 100644 --- a/plugins/core.c +++ b/plugins/core.c @@ -487,6 +487,45 @@ void qemu_plugin_register_atexit_cb(qemu_plugin_id_t id, plugin_register_cb_udata(id, QEMU_PLUGIN_EV_ATEXIT, cb, udata); } +/* + * Handle exit from linux-user. Unlike the normal atexit() mechanism + * we need to handle the clean-up manually as it's possible threads + * are still running. We need to remove all callbacks from code + * generation, flush the current translations and then we can safely + * trigger the exit callbacks. + */ + +void qemu_plugin_user_exit(void) +{ + enum qemu_plugin_event ev; + CPUState *cpu; + + QEMU_LOCK_GUARD(&plugin.lock); + + start_exclusive(); + + /* 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) { + struct qemu_plugin_ctx *ctx; + QTAILQ_FOREACH(ctx, &plugin.ctxs, entry) { + plugin_unregister_cb__locked(ctx, ev); + } + } + } + + tb_flush(current_cpu); + + CPU_FOREACH(cpu) { + qemu_plugin_disable_mem_helpers(cpu); + } + + end_exclusive(); + + /* now it's safe to handle the exit case */ + qemu_plugin_atexit_cb(); +} + /* * Call this function after longjmp'ing to the main loop. It's possible that the * last instruction of a TB might have used helpers, and therefore the