lkml.org 
[lkml]   [2010]   [Apr]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 4/7] hvc_console: Fix race between hvc_close and hvc_remove
On (Tue) Apr 06 2010 [21:42:38], Anton Blanchard wrote:
>
> 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.

OK, makes sense and since it works for you,

Acked-by: Amit Shah <amit.shah@redhat.com>

> 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>


\
 
 \ /
  Last update: 2010-04-06 14:13    [from the cache]
©2003-2011 Jasper Spaans