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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 <oleg@redhat.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2014-12-10 15:54:42 -08:00 committed by Linus Torvalds
parent 7117bc8888
commit 7f6def9f9b
1 changed files with 3 additions and 30 deletions
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33
kernel/kmod.c
View File

@ -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