From 5211613978cb7353a3237e4372958c0e7514683f Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Thu, 22 Oct 2015 13:32:08 -0700 Subject: [PATCH] kmod: don't run async usermode helper as a child of kworker thread 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. Fixes: bb304a5c6fc63d8506c ("kmod: handle UMH_WAIT_PROC from system unbound workqueue") Signed-off-by: Oleg Nesterov Acked-by: Frederic Weisbecker Cc: Rik van Riel Cc: Christoph Lameter Cc: Tejun Heo Cc: Rusty Russell Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/kmod.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/kernel/kmod.c b/kernel/kmod.c index da98d0593de2..0277d1216f80 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); -- 2.39.2