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Commit 11dbf203 authored by Arnd Bergmann's avatar Arnd Bergmann Committed by Greg Kroah-Hartman
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tty: avoid recursive BTM in pty_close 



When the console has been redirected, a hangup of the tty
will cause tty_release to be called under the big tty_mutex,
which leads to a deadlock because hangup is also called
under the BTM.

This moves the BTM deeper into the tty_hangup function so
we can close the redirected tty without holding the BTM.
In case of pty, we now need to drop the BTM before
calling tty_vhangup.

Signed-off-by: default avatarArnd Bergmann <arnd@arndb.de>
Acked-by: default avatarAlan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: John Kacur <jkacur@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent a0821df6

drivers/char/pty.c

+3 −1
Original line number Diff line number Diff line
@@ -62,7 +62,9 @@ static void pty_close(struct tty_struct *tty, struct file *filp) 
		if (tty->driver == ptm_driver)

			devpts_pty_kill(tty->link);

#endif

		tty_vhangup_locked(tty->link);

		tty_unlock();

		tty_vhangup(tty->link);

		tty_lock();

	}

}

drivers/char/tty_io.c

+12 −12
Original line number Diff line number Diff line
@@ -471,7 +471,7 @@ void tty_wakeup(struct tty_struct *tty) 
EXPORT_SYMBOL_GPL(tty_wakeup);



/**

 *	do_tty_hangup		-	actual handler for hangup events

 *	__tty_hangup		-	actual handler for hangup events

 *	@work: tty device

 *

 *	This can be called by the "eventd" kernel thread.  That is process
@@ -492,7 +492,7 @@ EXPORT_SYMBOL_GPL(tty_wakeup); 
 *		  tasklist_lock to walk task list for hangup event

 *		    ->siglock to protect ->signal/->sighand

 */

void tty_vhangup_locked(struct tty_struct *tty)

void __tty_hangup(struct tty_struct *tty)

{

	struct file *cons_filp = NULL;

	struct file *filp, *f = NULL;
@@ -512,10 +512,12 @@ void tty_vhangup_locked(struct tty_struct *tty) 
	}

	spin_unlock(&redirect_lock);



	tty_lock();



	/* inuse_filps is protected by the single tty lock,

	   this really needs to change if we want to flush the

	   workqueue with the lock held */

	check_tty_count(tty, "do_tty_hangup");

	check_tty_count(tty, "tty_hangup");



	file_list_lock();

	/* This breaks for file handles being sent over AF_UNIX sockets ? */
@@ -594,6 +596,9 @@ void tty_vhangup_locked(struct tty_struct *tty) 
	 */

	set_bit(TTY_HUPPED, &tty->flags);

	tty_ldisc_enable(tty);



	tty_unlock();



	if (f)

		fput(f);

}
@@ -603,9 +608,7 @@ static void do_tty_hangup(struct work_struct *work) 
	struct tty_struct *tty =

		container_of(work, struct tty_struct, hangup_work);



	tty_lock();

	tty_vhangup_locked(tty);

	tty_unlock();

	__tty_hangup(tty);

}



/**
@@ -643,13 +646,12 @@ void tty_vhangup(struct tty_struct *tty) 


	printk(KERN_DEBUG "%s vhangup...\n", tty_name(tty, buf));

#endif

	tty_lock();

	tty_vhangup_locked(tty);

	tty_unlock();

	__tty_hangup(tty);

}



EXPORT_SYMBOL(tty_vhangup);





/**

 *	tty_vhangup_self	-	process vhangup for own ctty

 *
@@ -727,10 +729,8 @@ void disassociate_ctty(int on_exit) 
	if (tty) {

		tty_pgrp = get_pid(tty->pgrp);

		if (on_exit) {

			tty_lock();

			if (tty->driver->type != TTY_DRIVER_TYPE_PTY)

				tty_vhangup_locked(tty);

			tty_unlock();

				tty_vhangup(tty);

		}

		tty_kref_put(tty);

	} else if (on_exit) {