1 files changed, 35 insertions, 2 deletions

diff --git a/kernel/kmod.c b/kernel/kmod.c
index ff2c7cb86d77..6f99aead66c6 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -45,6 +45,13 @@ 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
 
@@ -221,6 +228,13 @@ fail:
         return 0;
 }
 
+static int call_helper(void *data)
+{
+        /* Worker thread started blocking khelper thread. */
+        kmod_thread_locker = current;
+        return ____call_usermodehelper(data);
+}
+
 static void call_usermodehelper_freeinfo(struct subprocess_info *info)
 {
         if (info->cleanup)
@@ -295,9 +309,12 @@ static void __call_usermodehelper(struct work_struct *work)
         if (wait == UMH_WAIT_PROC)
                 pid = kernel_thread(wait_for_helper, sub_info,
                                     CLONE_FS | CLONE_FILES | SIGCHLD);
-        else
-                pid = kernel_thread(____call_usermodehelper, sub_info,
+        else {
+                pid = kernel_thread(call_helper, sub_info,
                                     CLONE_VFORK | SIGCHLD);
+                /* Worker thread stopped blocking khelper thread. */
+                kmod_thread_locker = NULL;
+        }
 
         switch (wait) {
         case UMH_NO_WAIT:
@@ -548,6 +565,16 @@ 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;
+        }
 
         sub_info->complete = &done;
         sub_info->wait = wait;
@@ -577,6 +604,12 @@ unlock:
         return retval;
 }
 
+/*
+ * call_usermodehelper_fns() will not run the caller-provided cleanup function
+ * if a memory allocation failure is experienced.  So the caller might need to
+ * check the call_usermodehelper_fns() return value: if it is -ENOMEM, perform
+ * the necessaary cleanup within the caller.
+ */
 int call_usermodehelper_fns(
         char *path, char **argv, char **envp, int wait,
         int (*init)(struct subprocess_info *info, struct cred *new),