From a729d2730d9d30f6610e43f070cedd1d60ba022f Mon Sep 17 00:00:00 2001
From: qihao <qihao@cmss.chinamobile.com>
Date: Thu, 30 Mar 2023 17:58:32 +0800
Subject: [PATCH] plugins: make qemu_plugin_user_exit's locking order
 consistent with fork_start's
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cheery-pick from 2bbbc1be8d9a21b25d0c80b9a7345074d54abd51

To fix potential deadlocks as reported by tsan.

Signed-off-by: qihao_yewu <qihao_yewu@cmss.chinamobile.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Emilio Cota <cota@braap.org>
Message-Id: <20230111151628.320011-6-cota@braap.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20230124180127.1881110-31-alex.bennee@linaro.org>
---
 plugins/core.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/plugins/core.c b/plugins/core.c
index 792262da08..e935e3c0c9 100644
--- a/plugins/core.c
+++ b/plugins/core.c
@@ -500,10 +500,18 @@ 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) {
@@ -514,12 +522,12 @@ 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 */
-- 
2.27.0