mdadm: Block SIGCHLD processes before starting children

There is a small race condition noticed during code review, but
never actully hit in practice, with the write_zero feature.

If a write zeros fork finishes quickly before wait_for_zero_forks()
gets called, then the SIGCHLD will be delivered before the signalfd
is setup.

While this is only theoretical, fix this by blocking the SIGCHLD
signal before forking any children.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/Create.c b/Create.c
index 4f992a22..bd4875e4 100644
--- a/Create.c
+++ b/Create.c
@@ -401,6 +401,7 @@ static int add_disks(int mdfd, struct mdinfo *info, struct shape *s,
 	 */
 	sigemptyset(&sigset);
 	sigaddset(&sigset, SIGINT);
+	sigaddset(&sigset, SIGCHLD);
 	sigprocmask(SIG_BLOCK, &sigset, &orig_sigset);
 	memset(zero_pids, 0, sizeof(zero_pids));