[PULL,23/31] main: keep rcu_atfork callback enabled for qtest

Commit Message

Stefan Hajnoczi Feb. 22, 2020, 8:50 a.m. UTC

From: Alexander Bulekov <[e-mail]>

The qtest-based fuzzer makes use of forking to reset-state between
tests. Keep the callback enabled, so the call_rcu thread gets created
within the child process.

Signed-off-by: Alexander Bulekov <[e-mail]>
Reviewed-by: Darren Kenny <[e-mail]>
Acked-by: Stefan Hajnoczi <[e-mail]>
Message-id: [e-mail]
Signed-off-by: Stefan Hajnoczi <[e-mail]>
---
 softmmu/vl.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

Patch

diff --git a/softmmu/vl.c b/softmmu/vl.c
index 080d3b5106..92c7b3a6e9 100644
--- a/softmmu/vl.c
+++ b/softmmu/vl.c
@@ -3782,7 +3782,17 @@  void qemu_init(int argc, char **argv, char **envp)
     set_memory_options(&ram_slots, &maxram_size, machine_class);
 
     os_daemonize();
-    rcu_disable_atfork();
+
+    /*
+     * If QTest is enabled, keep the rcu_atfork enabled, since system processes
+     * may be forked testing purposes (e.g. fork-server based fuzzing) The fork
+     * should happen before a signle cpu instruction is executed, to prevent
+     * deadlocks. See commit 73c6e40, rcu: "completely disable pthread_atfork
+     * callbacks as soon as possible"
+     */
+    if (!qtest_enabled()) {
+        rcu_disable_atfork();
+    }
 
     if (pid_file && !qemu_write_pidfile(pid_file, &err)) {
         error_reportf_err(err, "cannot create PID file: ");