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@xxxxxxxxxxxxxxxxxx>
---
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);
