Commit 7f6def9f authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

usermodehelper: kill the kmod_thread_locker logic 



Now that we do not call kernel_thread(CLONE_VFORK) from the worker
thread we can not deadlock if do_execve() in turn triggers another
call_usermodehelper(), we can remove the kmod_thread_locker code.

Note: we should probably kill khelper_wq and simply use one of the
global workqueues, say, system_unbound_wq, this special wq for umh buys
nothing nowadays.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7117bc88

kernel/kmod.c

+3 −30
Original line number Diff line number Diff line
@@ -47,13 +47,6 @@ extern int max_threads; 


static struct workqueue_struct *khelper_wq;



/*

 * kmod_thread_locker is used for deadlock avoidance.  There is no explicit

 * locking to protect this global - it is private to the singleton khelper

 * thread and should only ever be modified by that thread.

 */

static const struct task_struct *kmod_thread_locker;



#define CAP_BSET	(void *)1

#define CAP_PI		(void *)2
@@ -273,13 +266,6 @@ out: 
	do_exit(0);

}



static int call_helper(void *data)

{

	/* Worker thread started blocking khelper thread. */

	kmod_thread_locker = current;

	return ____call_usermodehelper(data);

}



/* Keventd can't block, but this (a child) can. */

static int wait_for_helper(void *data)

{
@@ -327,11 +313,9 @@ static void __call_usermodehelper(struct work_struct *work) 
	if (sub_info->wait & UMH_WAIT_PROC)

		pid = kernel_thread(wait_for_helper, sub_info,

				    CLONE_FS | CLONE_FILES | SIGCHLD);

	else {

		pid = kernel_thread(call_helper, sub_info, SIGCHLD);

		/* Worker thread stopped blocking khelper thread. */

		kmod_thread_locker = NULL;

	}

	else

		pid = kernel_thread(____call_usermodehelper, sub_info,

				    SIGCHLD);



	if (pid < 0) {

		sub_info->retval = pid;
@@ -564,17 +548,6 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait) 
		retval = -EBUSY;

		goto out;

	}

	/*

	 * Worker thread must not wait for khelper thread at below

	 * wait_for_completion() if the thread was created with CLONE_VFORK

	 * flag, for khelper thread is already waiting for the thread at

	 * wait_for_completion() in do_fork().

	 */

	if (wait != UMH_NO_WAIT && current == kmod_thread_locker) {

		retval = -EBUSY;

		goto out;

	}



	/*

	 * Set the completion pointer only if there is a waiter.

	 * This makes it possible to use umh_complete to free