Messages in this thread Patch in this message | | | Date | Tue, 8 Feb 2011 08:16:00 +1100 | From | Anton Blanchard <> | Subject | Re: [PATCH 21/23] hvc_console: Fix race between hvc_close and hvc_remove |
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Hi,
> From: Amit Shah <amit.shah@redhat.com> > > commit e74d098c66543d0731de62eb747ccd5b636a6f4c upstream. > > Alan pointed out a race in the code where hvc_remove is invoked. The > recent virtio_console work is the first user of hvc_remove().
I faintly remember this bug caused boot issues and the following patch must be applied to fix it.
Anton --
commit 320718ee074acce5ffced6506cb51af1388942aa Author: Anton Blanchard <anton@samba.org> Date: Tue Apr 6 21:42:38 2010 +1000
hvc_console: Fix race between hvc_close and hvc_remove
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> Acked-by: Amit Shah <amit.shah@redhat.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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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