[RFC] bloody odd logics in md_exit()

[Al Viro <viro@ZenIV.linux.org.uk>]

	Rationale in e2f23b606b94 (md: avoid oops on unload if some
process is in poll or select) is very odd.  Waitqueue code _does_
provide a way to remove all listeners from a waitqueue - it's simply
wake_up_all().  Once the wakeup callback has been executed (and it
runs in context of wake_up_all() caller), we don't *care* if md.o
is still there - all waiters are gone from the queue and the callback
(pollwake() and friends) doesn't reinsert them.

	Why do we need the entire md_unloading logics?  Just do
remove_proc_entry() (which will wait for any in-progress call of
->poll()) and then do plain wake_up_all().  Nothing new could get
added there once remove_proc_entry() is done and we don't need to
wake the waiters one-by-one, let alone play with exponential
backoffs for them to be gone from the queue...

	And while we are at it, procfs file_operations do not need
->owner - it's never looked at by anybody.

	Looks like the following would do just as well as the variant
currently in mainline and it's considerably simpler...  What am I
missing here?

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 63ceabb4e020..42ea44a809bd 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -7953,14 +7953,11 @@ static int md_seq_open(struct inode *inode, struct file *file)
 	return error;
 }
 
-static int md_unloading;
 static __poll_t mdstat_poll(struct file *filp, poll_table *wait)
 {
 	struct seq_file *seq = filp->private_data;
 	__poll_t mask;
 
-	if (md_unloading)
-		return EPOLLIN|EPOLLRDNORM|EPOLLERR|EPOLLPRI;
 	poll_wait(filp, &md_event_waiters, wait);
 
 	/* always allow read */
@@ -7972,7 +7969,6 @@ static __poll_t mdstat_poll(struct file *filp, poll_table *wait)
 }
 
 static const struct file_operations md_seq_fops = {
-	.owner		= THIS_MODULE,
 	.open           = md_seq_open,
 	.read           = seq_read,
 	.llseek         = seq_lseek,
@@ -9382,7 +9378,6 @@ static __exit void md_exit(void)
 {
 	struct mddev *mddev;
 	struct list_head *tmp;
-	int delay = 1;
 
 	blk_unregister_region(MKDEV(MD_MAJOR,0), 512);
 	blk_unregister_region(MKDEV(mdp_major,0), 1U << MINORBITS);
@@ -9392,17 +9387,8 @@ static __exit void md_exit(void)
 	unregister_reboot_notifier(&md_notifier);
 	unregister_sysctl_table(raid_table_header);
 
-	/* We cannot unload the modules while some process is
-	 * waiting for us in select() or poll() - wake them up
-	 */
-	md_unloading = 1;
-	while (waitqueue_active(&md_event_waiters)) {
-		/* not safe to leave yet */
-		wake_up(&md_event_waiters);
-		msleep(delay);
-		delay += delay;
-	}
 	remove_proc_entry("mdstat", NULL);
+	wake_up_all(&md_event_waiters);
 
 	for_each_mddev(mddev, tmp) {
 		export_array(mddev);