Messages in this thread Patch in this message | | | Date | Tue, 6 Apr 2010 21:42:38 +1000 | From | Anton Blanchard <> | Subject | Re: [PATCH 4/7] hvc_console: Fix race between hvc_close and hvc_remove |
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Hi,
> > Looking at the commit e74d098c66543d0731de62eb747ccd5b636a6f4c, > > i see that for every tty_kref_get() there is a corresponding > > tty_kref_put() except maybe for the one in the following patch snippet > > > > spin_lock_irqsave(&hp->lock, flags); > > /* Check and then increment for fast path open. */ > > if (hp->count++ > 0) { > > + tty_kref_get(tty); > > spin_unlock_irqrestore(&hp->lock, flags); > > hvc_kick(); > > return 0; > > > > I don't know this code very well but we might be missing a > > corresponding tty_kref_put() some place ? > > See hvc_hangup: > > temp_open_count = hp->count; > ... > while(temp_open_count) { > --temp_open_count; > tty_kref_put(tty); > kref_put(&hp->kref, destroy_hvc_struct); > }
I don't claim to understand the tty layer, but it seems like hvc_open and hvc_close should be balanced in their kref reference counting.
Right now we get a kref every call to hvc_open:
if (hp->count++ > 0) { tty_kref_get(tty); <----- here spin_unlock_irqrestore(&hp->lock, flags); hvc_kick(); return 0; } /* else count == 0 */
tty->driver_data = hp;
hp->tty = tty_kref_get(tty); <------ or here if hp->count was 0
But hvc_close has:
tty_kref_get(tty);
if (--hp->count == 0) { ... /* Put the ref obtained in hvc_open() */ tty_kref_put(tty); ... }
tty_kref_put(tty);
Since the outside kref get/put balance we only do a single kref_put when count reaches 0.
The patch below changes things to call tty_kref_put once for every hvc_close call, and with that my machine boots fine.
Signed-off-by: Anton Blanchard <anton@samba.org> ---
diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c index d3890e8..35cca4c 100644 --- a/drivers/char/hvc_console.c +++ b/drivers/char/hvc_console.c @@ -368,16 +368,12 @@ static void hvc_close(struct tty_struct *tty, struct file * filp) hp = tty->driver_data; spin_lock_irqsave(&hp->lock, flags); - tty_kref_get(tty); if (--hp->count == 0) { /* We are done with the tty pointer now. */ hp->tty = NULL; spin_unlock_irqrestore(&hp->lock, flags); - /* Put the ref obtained in hvc_open() */ - tty_kref_put(tty); - if (hp->ops->notifier_del) hp->ops->notifier_del(hp, hp->data);
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