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plugins: make qemu_plugin_user_exit's locking order consistent with fork_start's

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To fix potential deadlocks as reported by tsan.

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>
This commit is contained in:
Emilio Cota 2023-01-24 18:01:22 +00:00 committed by Alex Bennée
parent 68f7b2be53
commit 2bbbc1be8d
1 changed files with 11 additions and 5 deletions
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16
plugins/core.c
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@ -500,10 +500,17 @@ 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) {
@ -513,13 +520,12 @@ 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 */