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md: avoid oops on unload if some process is in poll or select.

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If md-mod is unloaded while some process is in poll() or select(),
then that process maintains a pointer to md_event_waiters, and when
the try to unlink from that list, they will oops.

The procfs infrastructure ensures that ->poll won't be called after
remove_proc_entry, but doesn't provide a wait_queue_head for us to
use, and the waitqueue code doesn't provide a way to remove all
listeners from a waitqueue.

So we need to:
 1/ make sure no further references to md_event_waiters are taken (by
    setting md_unloading)
 2/ wake up all processes currently waiting, and
 3/ wait until all those processes have disconnected from our
    wait_queue_head.

Reported-by: "majianpeng" <majianpeng@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.de>
This commit is contained in:
NeilBrown 2014-04-09 14:33:51 +10:00
parent da1aab3dca
commit e2f23b606b
1 changed files with 16 additions and 0 deletions
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16
drivers/md/md.c
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@ -7165,11 +7165,14 @@ static int md_seq_open(struct inode *inode, struct file *file)
return error;
}
static int md_unloading;
static unsigned int mdstat_poll(struct file *filp, poll_table *wait)
{
struct seq_file *seq = filp->private_data;
int mask;
if (md_unloading)
return POLLIN|POLLRDNORM|POLLERR|POLLPRI;;
poll_wait(filp, &md_event_waiters, wait);
/* always allow read */
@ -8655,6 +8658,7 @@ static __exit void md_exit(void)
{
struct mddev *mddev;
struct list_head *tmp;
int delay = 1;
blk_unregister_region(MKDEV(MD_MAJOR,0), 1U << MINORBITS);
blk_unregister_region(MKDEV(mdp_major,0), 1U << MINORBITS);
@ -8663,7 +8667,19 @@ static __exit void md_exit(void)
unregister_blkdev(mdp_major, "mdp");
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);
for_each_mddev(mddev, tmp) {
export_array(mddev);
mddev->hold_active = 0;