From f7e68c9c99ad94f23d3ba3af1642c805b11c71c1 Mon Sep 17 00:00:00 2001 From: Alex Bennée Date: Wed, 21 Jul 2021 00:26:54 +0100 Subject: tcg/plugins: implement a qemu_plugin_user_exit helper MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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: <20210720232703.10650-21-alex.bennee@linaro.org> --- include/qemu/plugin.h | 12 ++++++++++++ include/qemu/qemu-plugin.h | 13 +++++++++++++ 2 files changed, 25 insertions(+) (limited to 'include/qemu') 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); -- cgit 1.4.1