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From: "Alex Bennée" <alex.bennee@linaro.org>
To: qemu-devel@nongnu.org
Cc: fam@euphon.net, berrange@redhat.com,
	"Kyle Evans" <kevans@freebsd.org>,
	f4bug@amsat.org, "Laurent Vivier" <laurent@vivier.eu>,
	"Warner Losh" <imp@bsdimp.com>,
	stefanha@redhat.com, crosa@redhat.com, pbonzini@redhat.com,
	"Mahmoud Mandour" <ma.mandourr@gmail.com>,
	"Alexandre Iooss" <erdnaxe@crans.org>,
	"Alex Bennée" <alex.bennee@linaro.org>,
	aurelien@aurel32.net
Subject: [PATCH v1 20/29] tcg/plugins: implement a qemu_plugin_user_exit helper
Date: Wed, 21 Jul 2021 00:26:54 +0100	[thread overview]
Message-ID: <20210720232703.10650-21-alex.bennee@linaro.org> (raw)
In-Reply-To: <20210720232703.10650-1-alex.bennee@linaro.org>

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 <alex.bennee@linaro.org>
Reviewed-by: Mahmoud Mandour <ma.mandourr@gmail.com>
Acked-by: Warner Losh <imp@bsdimp.com>
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
-- 
2.32.0.264.g75ae10bc75



  parent reply	other threads:[~2021-07-20 23:53 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-20 23:26 [PATCH for 6.1-rc1 v1 00/29] various fixes pre-PR (metadata, docs, plugins, testing) Alex Bennée
2021-07-20 23:26 ` [PATCH v1 01/29] gitignore: Update with some filetypes Alex Bennée
2021-07-20 23:26 ` [PATCH v1 02/29] docs: collect the disparate device emulation docs into one section Alex Bennée
2021-07-21 13:25   ` Markus Armbruster
2021-07-20 23:26 ` [PATCH v1 03/29] docs: add a section on the generalities of vhost-user Alex Bennée
2021-07-20 23:26 ` [PATCH v1 04/29] configure: remove needless if leg Alex Bennée
2021-07-20 23:26 ` [PATCH v1 05/29] contrib/gitdm: add some new aliases to fix up commits Alex Bennée
2021-07-20 23:26 ` [PATCH v1 06/29] .mailmap: fix up some broken commit authors Alex Bennée
2021-07-20 23:26 ` [PATCH v1 07/29] contrib/gitdm: add domain-map for MontaVista Alex Bennée
2021-07-20 23:26 ` [PATCH v1 08/29] contrib/gitdm: add a group mapping for robot scanners Alex Bennée
2021-07-20 23:26 ` [PATCH v1 09/29] gitdm.config: sort the corporate GroupMap entries Alex Bennée
2021-07-21  8:06   ` Philippe Mathieu-Daudé
2021-07-20 23:26 ` [PATCH v1 10/29] contrib/gitdm: add domain-map/group-map mappings for Samsung Alex Bennée
2021-07-20 23:26 ` [PATCH v1 11/29] contrib/gitdm: add domain-map for Eldorado Alex Bennée
2021-07-20 23:26 ` [PATCH v1 12/29] contrib/gitdm: add domain-map/group-map for Wind River Alex Bennée
2021-07-20 23:26 ` [PATCH v1 13/29] contrib/gitdm: un-ironically add a mapping for LWN Alex Bennée
2021-07-20 23:26 ` [PATCH v1 14/29] contrib/gitdm: add domain-map for Crudebyte Alex Bennée
2021-07-20 23:26 ` [PATCH v1 15/29] contrib/gitdm: add domain-map for NVIDIA Alex Bennée
2021-07-20 23:26 ` [PATCH v1 16/29] contrib/gitdm: add group-map for Netflix Alex Bennée
2021-07-20 23:26 ` [PATCH v1 17/29] contrib/gitdm: add an explicit academic entry for BU Alex Bennée
2021-07-20 23:26 ` [PATCH v1 18/29] contrib/gitdm: add a new interns group-map for GSoC/Outreachy work Alex Bennée
2021-07-20 23:26 ` [PATCH v1 19/29] contrib/gitdm: add more individual contributor entries Alex Bennée
2021-07-20 23:26 ` Alex Bennée [this message]
2021-07-20 23:26 ` [PATCH v1 21/29] plugins/cache: Fixed a bug with destroying FIFO metadata Alex Bennée
2021-07-20 23:26 ` [PATCH v1 22/29] plugins/cache: limited the scope of a mutex lock Alex Bennée
2021-07-20 23:26 ` [PATCH v1 23/29] plugins/cache: Fixed "function decl. is not a prototype" warnings Alex Bennée
2021-07-21  8:09   ` Philippe Mathieu-Daudé
2021-07-20 23:26 ` [PATCH v1 24/29] plugins: Fix physical address calculation for IO regions Alex Bennée
2021-07-20 23:26 ` [PATCH v1 25/29] hw/tricore: fix inclusion of tricore_testboard Alex Bennée
2021-08-02 16:07   ` Bastian Koppelmann
2021-07-20 23:27 ` [PATCH v1 26/29] tests/tcg/configure.sh: add handling for assembler only builds Alex Bennée
2021-07-20 23:27 ` [PATCH v1 27/29] gitlab: enable a very minimal build with the tricore container Alex Bennée
2021-07-21  7:05   ` Thomas Huth
2021-07-21 15:00   ` Willian Rampazzo
2021-07-20 23:27 ` [PATCH v1 28/29] gitlab-ci: Remove the second superfluous macos task Alex Bennée
2021-07-20 23:27 ` [PATCH v1 29/29] gitlab-ci: Extract OpenSBI job rules to reusable section Alex Bennée

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