From 7f6def9f9b6ebba42fcdc12cfb3092f2cf44b3fe Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Wed, 10 Dec 2014 15:54:42 -0800 Subject: [PATCH] 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: Oleg Nesterov Cc: Martin Schwidefsky Cc: Oleg Nesterov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/kmod.c | 33 +++------------------------------ 1 file changed, 3 insertions(+), 30 deletions(-) diff --git a/kernel/kmod.c b/kernel/kmod.c index 4621771b43b9..2777f40a9c7b 100644 --- a/kernel/kmod.c +++ b/kernel/kmod.c @@ -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