[PATCH 0/2] fix deadlock with plugins reset/uninstall

[PATCH 0/2] fix deadlock with plugins reset/uninstall

[Pierrick Bouvier]

We first fix the issue reported in [1].
We then add a test plugin making sure we don't regress in the future.

[1] https://gitlab.com/qemu-project/qemu/-/issues/2901

Pierrick Bouvier (2):
  plugins/loader: fix deadlock when resetting/uninstalling a plugin
  tests/tcg/plugins: add plugin to test reset and uninstall

 plugins/loader.c              |  2 +-
 tests/tcg/plugins/reset.c     | 73 +++++++++++++++++++++++++++++++++++
 tests/tcg/plugins/meson.build |  2 +-
 3 files changed, 75 insertions(+), 2 deletions(-)
 create mode 100644 tests/tcg/plugins/reset.c

-- 
2.39.5

[PATCH 1/2] plugins/loader: fix deadlock when resetting/uninstalling a plugin

[Pierrick Bouvier]

Reported and fixed by Dmitry Kurakin.

Fixes: https://gitlab.com/qemu-project/qemu/-/issues/2901
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
---
 plugins/loader.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/plugins/loader.c b/plugins/loader.c
index 7523d554f03..0d6e082e170 100644
--- a/plugins/loader.c
+++ b/plugins/loader.c
@@ -370,7 +370,7 @@ static void plugin_reset_destroy(struct qemu_plugin_reset_data *data)
 {
     qemu_rec_mutex_lock(&plugin.lock);
     plugin_reset_destroy__locked(data);
-    qemu_rec_mutex_lock(&plugin.lock);
+    qemu_rec_mutex_unlock(&plugin.lock);
 }
 
 static void plugin_flush_destroy(CPUState *cpu, run_on_cpu_data arg)
-- 
2.39.5

Re: [PATCH 1/2] plugins/loader: fix deadlock when resetting/uninstalling a plugin

[Philippe Mathieu-Daudé]

On 4/4/25 05:20, Pierrick Bouvier wrote:
> Reported and fixed by Dmitry Kurakin.
> 

Fixes: 54cb65d8588 ("plugin: add core code")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2901
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

> Fixes: https://gitlab.com/qemu-project/qemu/-/issues/2901
> Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
> ---
>   plugins/loader.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

[PATCH 2/2] tests/tcg/plugins: add plugin to test reset and uninstall

[Pierrick Bouvier]

We perform a plugin reset, uninstall, and make sure we went through
those steps.

Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
---
 tests/tcg/plugins/reset.c     | 73 +++++++++++++++++++++++++++++++++++
 tests/tcg/plugins/meson.build |  2 +-
 2 files changed, 74 insertions(+), 1 deletion(-)
 create mode 100644 tests/tcg/plugins/reset.c

diff --git a/tests/tcg/plugins/reset.c b/tests/tcg/plugins/reset.c
new file mode 100644
index 00000000000..1be8be2a4b2
--- /dev/null
+++ b/tests/tcg/plugins/reset.c
@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) 2025 Linaro Ltd
+ *
+ * Test the reset/uninstall cycle of a plugin.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+#include <glib.h>
+
+#include <qemu-plugin.h>
+
+QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION;
+static qemu_plugin_id_t plugin_id;
+static bool was_reset;
+static bool was_uninstalled;
+
+static void after_uninstall(qemu_plugin_id_t id)
+{
+    g_assert(was_reset && !was_uninstalled);
+    qemu_plugin_outs("uninstall done\n");
+    was_uninstalled = true;
+}
+
+static void tb_exec_after_reset(unsigned int vcpu_index, void *userdata)
+{
+    g_assert(was_reset && !was_uninstalled);
+    qemu_plugin_uninstall(plugin_id, after_uninstall);
+}
+
+static void tb_trans_after_reset(qemu_plugin_id_t id, struct qemu_plugin_tb *tb)
+{
+    g_assert(was_reset && !was_uninstalled);
+    qemu_plugin_register_vcpu_tb_exec_cb(tb, tb_exec_after_reset,
+                                         QEMU_PLUGIN_CB_NO_REGS, NULL);
+}
+
+static void after_reset(qemu_plugin_id_t id)
+{
+    g_assert(!was_reset && !was_uninstalled);
+    qemu_plugin_outs("reset done\n");
+    was_reset = true;
+    qemu_plugin_register_vcpu_tb_trans_cb(id, tb_trans_after_reset);
+}
+
+static void tb_exec_before_reset(unsigned int vcpu_index, void *userdata)
+{
+    g_assert(!was_reset && !was_uninstalled);
+    qemu_plugin_reset(plugin_id, after_reset);
+}
+
+static void tb_trans_before_reset(qemu_plugin_id_t id, struct qemu_plugin_tb *tb)
+{
+    g_assert(!was_reset && !was_uninstalled);
+    qemu_plugin_register_vcpu_tb_exec_cb(tb, tb_exec_before_reset,
+                                         QEMU_PLUGIN_CB_NO_REGS, NULL);
+}
+
+QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id,
+                                           const qemu_info_t *info,
+                                           int argc, char **argv)
+{
+    plugin_id = id;
+    qemu_plugin_register_vcpu_tb_trans_cb(id, tb_trans_before_reset);
+    return 0;
+}
+
+/* Since we uninstall the plugin, we can't use qemu_plugin_register_atexit_cb,
+ * so we use destructor attribute instead. */
+static void __attribute__((destructor)) on_plugin_exit(void)
+{
+    g_assert(was_reset && was_uninstalled);
+    qemu_plugin_outs("plugin exit\n");
+}
diff --git a/tests/tcg/plugins/meson.build b/tests/tcg/plugins/meson.build
index c8cb0626a6d..41f02f2c7fa 100644
--- a/tests/tcg/plugins/meson.build
+++ b/tests/tcg/plugins/meson.build
@@ -1,6 +1,6 @@
 t = []
 if get_option('plugins')
-  foreach i : ['bb', 'empty', 'inline', 'insn', 'mem', 'syscall']
+  foreach i : ['bb', 'empty', 'inline', 'insn', 'mem', 'reset', 'syscall']
     if host_os == 'windows'
       t += shared_module(i, files(i + '.c') + '../../../contrib/plugins/win32_linker.c',
                         include_directories: '../../../include/qemu',
-- 
2.39.5

Re: [PATCH 0/2] fix deadlock with plugins reset/uninstall

[Alex Bennée]

Pierrick Bouvier <pierrick.bouvier@linaro.org> writes:

> We first fix the issue reported in [1].
> We then add a test plugin making sure we don't regress in the future.
>
> [1] https://gitlab.com/qemu-project/qemu/-/issues/2901

Queued to plugins/next, thanks.

>
> Pierrick Bouvier (2):
>   plugins/loader: fix deadlock when resetting/uninstalling a plugin
>   tests/tcg/plugins: add plugin to test reset and uninstall
>
>  plugins/loader.c              |  2 +-
>  tests/tcg/plugins/reset.c     | 73 +++++++++++++++++++++++++++++++++++
>  tests/tcg/plugins/meson.build |  2 +-
>  3 files changed, 75 insertions(+), 2 deletions(-)
>  create mode 100644 tests/tcg/plugins/reset.c

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro