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, 17 insertions, 14 deletions

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 7297acfe520c..83e9e7d9b58c 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -1254,7 +1254,7 @@ EXPORT_SYMBOL_GPL(tty_ldisc_flush);
         
 /**
  *      do_tty_hangup           -       actual handler for hangup events
- *      @data: tty device
+ *      @work: tty device
  *
  *      This can be called by the "eventd" kernel thread.  That is process
  *      synchronous but doesn't hold any locks, so we need to make sure we
@@ -1274,9 +1274,10 @@ EXPORT_SYMBOL_GPL(tty_ldisc_flush);
  *              tasklist_lock to walk task list for hangup event
  *
  */
-static void do_tty_hangup(void *data)
+static void do_tty_hangup(struct work_struct *work)
 {
-        struct tty_struct *tty = (struct tty_struct *) data;
+        struct tty_struct *tty =
+                container_of(work, struct tty_struct, hangup_work);
         struct file * cons_filp = NULL;
         struct file *filp, *f = NULL;
         struct task_struct *p;
@@ -1433,7 +1434,7 @@ void tty_vhangup(struct tty_struct * tty)
 
         printk(KERN_DEBUG "%s vhangup...\n", tty_name(tty, buf));
 #endif
-        do_tty_hangup((void *) tty);
+        do_tty_hangup(&tty->hangup_work);
 }
 EXPORT_SYMBOL(tty_vhangup);
 
@@ -3304,12 +3305,13 @@ int tty_ioctl(struct inode * inode, struct file * file,
  * Nasty bug: do_SAK is being called in interrupt context.  This can
  * deadlock.  We punt it up to process context.  AKPM - 16Mar2001
  */
-static void __do_SAK(void *arg)
+static void __do_SAK(struct work_struct *work)
 {
+        struct tty_struct *tty =
+                container_of(work, struct tty_struct, SAK_work);
 #ifdef TTY_SOFT_SAK
         tty_hangup(tty);
 #else
-        struct tty_struct *tty = arg;
         struct task_struct *g, *p;
         int session;
         int             i;
@@ -3388,7 +3390,7 @@ void do_SAK(struct tty_struct *tty)
 {
         if (!tty)
                 return;
-        PREPARE_WORK(&tty->SAK_work, __do_SAK, tty);
+        PREPARE_WORK(&tty->SAK_work, __do_SAK);
         schedule_work(&tty->SAK_work);
 }
 
@@ -3396,7 +3398,7 @@ EXPORT_SYMBOL(do_SAK);
 
 /**
  *      flush_to_ldisc
- *      @private_: tty structure passed from work queue.
+ *      @work: tty structure passed from work queue.
  *
  *      This routine is called out of the software interrupt to flush data
  *      from the buffer chain to the line discipline.
@@ -3406,9 +3408,10 @@ EXPORT_SYMBOL(do_SAK);
  *      receive_buf method is single threaded for each tty instance.
  */
  
-static void flush_to_ldisc(void *private_)
+static void flush_to_ldisc(struct work_struct *work)
 {
-        struct tty_struct *tty = (struct tty_struct *) private_;
+        struct tty_struct *tty =
+                container_of(work, struct tty_struct, buf.work.work);
         unsigned long   flags;
         struct tty_ldisc *disc;
         struct tty_buffer *tbuf, *head;
@@ -3553,7 +3556,7 @@ void tty_flip_buffer_push(struct tty_struct *tty)
         spin_unlock_irqrestore(&tty->buf.lock, flags);
 
         if (tty->low_latency)
-                flush_to_ldisc((void *) tty);
+                flush_to_ldisc(&tty->buf.work.work);
         else
                 schedule_delayed_work(&tty->buf.work, 1);
 }
@@ -3580,17 +3583,17 @@ static void initialize_tty_struct(struct tty_struct *tty)
         tty->overrun_time = jiffies;
         tty->buf.head = tty->buf.tail = NULL;
         tty_buffer_init(tty);
-        INIT_DELAYED_WORK(&tty->buf.work, flush_to_ldisc, tty);
+        INIT_DELAYED_WORK(&tty->buf.work, flush_to_ldisc);
         init_MUTEX(&tty->buf.pty_sem);
         mutex_init(&tty->termios_mutex);
         init_waitqueue_head(&tty->write_wait);
         init_waitqueue_head(&tty->read_wait);
-        INIT_WORK(&tty->hangup_work, do_tty_hangup, tty);
+        INIT_WORK(&tty->hangup_work, do_tty_hangup);
         mutex_init(&tty->atomic_read_lock);
         mutex_init(&tty->atomic_write_lock);
         spin_lock_init(&tty->read_lock);
         INIT_LIST_HEAD(&tty->tty_files);
-        INIT_WORK(&tty->SAK_work, NULL, NULL);
+        INIT_WORK(&tty->SAK_work, NULL);
 }
 
 /*