From d6919e4cb65230b0c8081eb072893d4e8a191a59 Mon Sep 17 00:00:00 2001 From: Alexander Bulekov Date: Wed, 19 Feb 2020 23:11:10 -0500 Subject: [PATCH] main: keep rcu_atfork callback enabled for qtest 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 Reviewed-by: Darren Kenny Acked-by: Stefan Hajnoczi Message-id: 20200220041118.23264-15-alxndr@bu.edu Signed-off-by: Stefan Hajnoczi --- softmmu/vl.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) 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: ");