WorkStruct: Pass the work_struct pointer instead of context data

Pass the work_struct pointer to the work function rather than context data.
The work function can use container_of() to work out the data.

For the cases where the container of the work_struct may go away the moment the
pending bit is cleared, it is made possible to defer the release of the
structure by deferring the clearing of the pending bit.

To make this work, an extra flag is introduced into the management side of the
work_struct.  This governs auto-release of the structure upon execution.

Ordinarily, the work queue executor would release the work_struct for further
scheduling or deallocation by clearing the pending bit prior to jumping to the
work function.  This means that, unless the driver makes some guarantee itself
that the work_struct won't go away, the work function may not access anything
else in the work_struct or its container lest they be deallocated..  This is a
problem if the auxiliary data is taken away (as done by the last patch).

However, if the pending bit is *not* cleared before jumping to the work
function, then the work function *may* access the work_struct and its container
with no problems.  But then the work function must itself release the
work_struct by calling work_release().

In most cases, automatic release is fine, so this is the default.  Special
initiators exist for the non-auto-release case (ending in _NAR).


Signed-Off-By: David Howells <dhowells@redhat.com>

1 files changed, 10 insertions, 6 deletions

diff --git a/kernel/kmod.c b/kernel/kmod.c
index bb4e29d924e4..7dc7a9dad6ac 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -114,6 +114,7 @@ EXPORT_SYMBOL(request_module);
 #endif /* CONFIG_KMOD */
 
 struct subprocess_info {
+        struct work_struct work;
         struct completion *complete;
         char *path;
         char **argv;
@@ -221,9 +222,10 @@ static int wait_for_helper(void *data)
 }
 
 /* This is run by khelper thread  */
-static void __call_usermodehelper(void *data)
+static void __call_usermodehelper(struct work_struct *work)
 {
-        struct subprocess_info *sub_info = data;
+        struct subprocess_info *sub_info =
+                container_of(work, struct subprocess_info, work);
         pid_t pid;
         int wait = sub_info->wait;
 
@@ -264,6 +266,8 @@ int call_usermodehelper_keys(char *path, char **argv, char **envp,
 {
         DECLARE_COMPLETION_ONSTACK(done);
         struct subprocess_info sub_info = {
+                .work           = __WORK_INITIALIZER(sub_info.work,
+                                                     __call_usermodehelper),
                 .complete       = &done,
                 .path           = path,
                 .argv           = argv,
@@ -272,7 +276,6 @@ int call_usermodehelper_keys(char *path, char **argv, char **envp,
                 .wait           = wait,
                 .retval         = 0,
         };
-        DECLARE_WORK(work, __call_usermodehelper, &sub_info);
 
         if (!khelper_wq)
                 return -EBUSY;
@@ -280,7 +283,7 @@ int call_usermodehelper_keys(char *path, char **argv, char **envp,
         if (path[0] == '\0')
                 return 0;
 
-        queue_work(khelper_wq, &work);
+        queue_work(khelper_wq, &sub_info.work);
         wait_for_completion(&done);
         return sub_info.retval;
 }
@@ -291,6 +294,8 @@ int call_usermodehelper_pipe(char *path, char **argv, char **envp,
 {
         DECLARE_COMPLETION(done);
         struct subprocess_info sub_info = {
+                .work           = __WORK_INITIALIZER(sub_info.work,
+                                                     __call_usermodehelper),
                 .complete       = &done,
                 .path           = path,
                 .argv           = argv,
@@ -298,7 +303,6 @@ int call_usermodehelper_pipe(char *path, char **argv, char **envp,
                 .retval         = 0,
         };
         struct file *f;
-        DECLARE_WORK(work, __call_usermodehelper, &sub_info);
 
         if (!khelper_wq)
                 return -EBUSY;
@@ -318,7 +322,7 @@ int call_usermodehelper_pipe(char *path, char **argv, char **envp,
         }
         sub_info.stdin = f;
 
-        queue_work(khelper_wq, &work);
+        queue_work(khelper_wq, &sub_info.work);
         wait_for_completion(&done);
         return sub_info.retval;
 }