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Subject: PATCH: Lock tty directly in acct layer
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: akpm@osdl.org, linux-kernel@vger.kernel.org
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Date: Wed, 16 Aug 2006 17:36:41 +0100
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Signed-off-by: Alan Cox <alan@redhat.com>

diff -u --new-file --recursive --exclude-from /usr/src/exclude linux.vanilla-2.6.18-rc4-mm1/kernel/acct.c linux-2.6.18-rc4-mm1/kernel/acct.c
--- linux.vanilla-2.6.18-rc4-mm1/kernel/acct.c	2006-08-15 15:40:19.000000000 +0100
+++ linux-2.6.18-rc4-mm1/kernel/acct.c	2006-08-15 16:03:18.000000000 +0100
@@ -483,10 +484,10 @@
 	ac.ac_ppid = current->parent->tgid;
 #endif
 
-	read_lock(&tasklist_lock);	/* pin current->signal */
+	mutex_lock(&tty_mutex);
 	ac.ac_tty = current->signal->tty ?
 		old_encode_dev(tty_devnum(current->signal->tty)) : 0;
-	read_unlock(&tasklist_lock);
+	mutex_unlock(&tty_mutex);
 
 	spin_lock_irq(&current->sighand->siglock);
 	ac.ac_utime = encode_comp_t(jiffies_to_AHZ(cputime_to_jiffies(pacct->ac_utime)));