BUG in tty_open when using containers and ptrace

[Grzegorz Nosek]

On czw, lip 23, 2009 at 12:32:45 -0700, Sukadev Bhattiprolu wrote:
> | OK, the first bad commit is:
> | commit 4a2b5fddd53b80efcb3266ee36e23b8de28e761a
> 
> Yes, I think this was fixed by 808ffa3d302257b9dc37b1412c1fcdf976fcddac

Any other tests I can do that will be helpful? E.g. 2.6.27 + 808ffa?

> | The oops itself is introduced by:
> | commit 527b3e4773628b30d03323a2cb5fb0d84441990f
> | Author: Sukadev Bhattiprolu <sukadev at us.ibm.com>
> | Date:   Mon Oct 13 10:43:08 2008 +0100
> | 
> |     Simplify devpts_get_tty()
> | 
> |     As pointed out by H. Peter Anvin, since the inode for the pty is known,
> |     we don't need to look it up.
> | 
> |     Signed-off-by: Sukadev Bhattiprolu <sukadev at us.ibm.com>
> |     Signed-off-by: Alan Cox <alan at redhat.com>
> |     Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
> 
> Maybe before returning the tty, we need to take an extra reference on
> the dentry.

I tried that and while it did not oops, I wasn't sure where to dput it
back, so it leaked like a sieve. I'm probably missing something obvious
but I couldn't find a function whose calls balanced calls to
devpts_get_tty.

BTW, what would the semantics be? I.e. what can we do with a pty that has
its master side long gone?

Best regards,
 Grzegorz Nosek