From cbe9352fa08f90aa03b4dbf1bbabfc95d196e562 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Mon, 3 Aug 2009 14:54:56 -0700
Subject: [PATCH] tty-ldisc: be more careful in 'put_ldisc' locking

Use 'atomic_dec_and_lock()' to make sure that we always hold the
tty_ldisc_lock when the ldisc count goes to zero. That way we can never
race against 'tty_ldisc_try()' increasing the count again.

Reported-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Tested-by: Sergey Senozhatsky <sergey.senozhatsky@mail.by>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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