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kmod: don't run async usermode helper as a child of kworker thread

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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: bb304a5c6f ("kmod: handle UMH_WAIT_PROC from system unbound workqueue")
Signed-off-by: Oleg Nesterov <[email protected]>
Acked-by: Frederic Weisbecker <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Rusty Russell <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Oleg Nesterov 2015-10-22 13:32:08 -07:00 • committed by Linus Torvalds
commit 5211613978
1 changed files with 6 additions and 2 deletions
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8
kernel/kmod.c
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@ -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);