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authorPeter Maydell <peter.maydell@linaro.org>2017-12-07 12:41:21 +0000
committerLaurent Vivier <laurent@vivier.eu>2018-01-23 14:20:52 +0100
commit06065c451f10c7ef62cfb575a87f323a70ae1c9e (patch)
treed3c378e1c2edb830504a28487d14e0add05b9e2f /linux-user
parent024949caf32805f4cc3e7d363a80084b47aac1f6 (diff)
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linux-user: wrap fork() in a start/end exclusive section
When we do a fork() in usermode emulation, we need to be in a start/end exclusive section, so that we can ensure that no other thread is in an RCU section. Otherwise you can get this deadlock: - fork thread: has mmap_lock, waits for rcu_sync_lock (because rcu_init_lock() is registered as a pthread_atfork() hook) - RCU thread: has rcu_sync_lock, waits for rcu_read_(un)lock - another CPU thread: in RCU critical section, waits for mmap_lock This can show up if you have a heavily multithreaded guest program that does a fork(). Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reported-by: Stuart Monteith <stuart.monteith@linaro.org> Message-Id: <1512650481-1723-1-git-send-email-peter.maydell@linaro.org> Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Diffstat (limited to 'linux-user')
-rw-r--r--linux-user/main.c5
1 files changed, 5 insertions, 0 deletions
diff --git a/linux-user/main.c b/linux-user/main.c
index e840691..2140465 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -127,6 +127,7 @@ int cpu_get_pic_interrupt(CPUX86State *env)
/* Make sure everything is in a consistent state for calling fork(). */
void fork_start(void)
{
+ start_exclusive();
mmap_fork_start();
qemu_mutex_lock(&tb_ctx.tb_lock);
cpu_list_lock();
@@ -147,9 +148,13 @@ void fork_end(int child)
qemu_mutex_init(&tb_ctx.tb_lock);
qemu_init_cpu_list();
gdbserver_fork(thread_cpu);
+ /* qemu_init_cpu_list() takes care of reinitializing the
+ * exclusive state, so we don't need to end_exclusive() here.
+ */
} else {
qemu_mutex_unlock(&tb_ctx.tb_lock);
cpu_list_unlock();
+ end_exclusive();
}
}