linux-kernel - [PATCH 09/68] TTY: tty_driver, document tty->ops->shutdown limitation

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Date:	Mon,  5 Mar 2012 14:51:56 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	gregkh@...uxfoundation.org
Cc:	alan@...ux.intel.com, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org, jirislaby@...il.com
Subject: [PATCH 09/68] TTY: tty_driver, document tty->ops->shutdown limitation

Note that tty->ops->shutdown is called from whatever context the user
drops the last tty reference from. E.g. if one takes a reference in
an ISR, tty close happens on other CPU and the final tty put is from
the ISR, tty->ops->shutdown will be called from that hard irq context.

We would have a problem in vt if we start using tty refcounting from
other contexts than user there. It is because vt's shutdown uses
mutexes. This is yet to be fixed.

Signed-off-by: Jiri Slaby <jslaby@...e.cz>
Reported-by: Al Viro <viro@...iv.linux.org.uk>
---
 include/linux/tty_driver.h |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/tty_driver.h b/include/linux/tty_driver.h
index e064f17..6e6dbb7 100644
--- a/include/linux/tty_driver.h
+++ b/include/linux/tty_driver.h
@@ -50,6 +50,8 @@
  *	Note that tty_shutdown() is not called if ops->shutdown is defined.
  *	This means one is responsible to take care of calling ops->remove (e.g.
  *	via tty_driver_remove_tty) and releasing tty->termios.
+ *	Note that this hook may be called from *all* the contexts where one
+ *	uses tty refcounting (e.g. tty_port_tty_get).
  *
  *
  * void (*cleanup)(struct tty_struct * tty);
-- 
1.7.9.2


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