call_usermodehelper_exec_sync() does fork() + wait() with "unignored"
SIGCHLD. What we have missed is that this worker thread can have other
children previously forked by call_usermodehelper_exec_work() without
UMH_WAIT_PROC. If such a child exits in between it becomes a zombie
because auto-reaping only works if SIGCHLD is ignored, and nobody can
reap it (unless/until this worker thread exits too).
Change the !UMH_WAIT_PROC case to use CLONE_PARENT.
Note: this is only first step. All PF_KTHREAD tasks, even created by
kernel_thread() should have ->parent == kthreadd by default.
Signed-off-by: Oleg Nesterov <o...@redhat.com>
---
kernel/kmod.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/kernel/kmod.c b/kernel/kmod.c
index da98d05..0277d12 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -327,9 +327,13 @@ static void call_usermodehelper_exec_work(struct
work_struct *work)
call_usermodehelper_exec_sync(sub_info);
} else {
pid_t pid;
-
+ /*
+ * Use CLONE_PARENT to reparent it to kthreadd; we do not
+ * want to pollute current->children, and we need a parent
+ * that always ignores SIGCHLD to ensure auto-reaping.
+ */
pid = kernel_thread(call_usermodehelper_exec_async, sub_info,
- SIGCHLD);
+ CLONE_PARENT | SIGCHLD);
if (pid < 0) {
sub_info->retval = pid;
umh_complete(sub_info);
--
2.4.3
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