Commit 52116139 authored Oct 22, 2015 by Oleg Nesterov Committed by Linus Torvalds Oct 23, 2015

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: bb304a5c ("kmod: handle UMH_WAIT_PROC from system unbound workqueue")
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 8a70dd26

kernel/kmod.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -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);

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