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tty: Replace ldisc locking with ldisc_sem

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Line discipline locking was performed with a combination of
a mutex, a status bit, a count, and a waitqueue -- basically,
a rw semaphore.

Replace the existing combination with an ld_semaphore.

Fixes:
 1) the 'reference acquire after ldisc locked' bug
 2) the over-complicated halt mechanism
 3) lock order wrt. tty_lock()
 4) dropping locks while changing ldisc
 5) previously unidentified deadlock while locking ldisc from
    both linked ttys concurrently
 6) previously unidentified recursive deadlocks

Adds much-needed lockdep diagnostics.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley 2013-06-15 07:04:48 -04:00 • committed by Greg Kroah-Hartman
parent d2c438905f
commit 36697529b5
5 changed files with 52 additions and 293 deletions
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2
drivers/tty/tty_buffer.c
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@ -429,7 +429,7 @@ static void flush_to_ldisc(struct work_struct *work)
return;
disc = tty_ldisc_ref(tty);
if (disc == NULL) /* !TTY_LDISC */
if (disc == NULL)
return;
spin_lock_irqsave(&buf->lock, flags);