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Subject[PATCH 2/2] 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>
---
kernel/kmod.c | 33 +++------------------------------
1 files changed, 3 insertions(+), 30 deletions(-)

diff --git a/kernel/kmod.c b/kernel/kmod.c
index 4621771..2777f40 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;
@@ -565,17 +549,6 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait)
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
* the data structure in case of UMH_NO_WAIT.
--
1.5.5.1



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