Commit c65c9bc3 authored by Alan Cox's avatar Alan Cox Committed by Linus Torvalds
Browse files

tty: rewrite the ldisc locking 



There are several pretty much unfixable races in the old ldisc code, especially
with respect to pty behaviour and also to hangup. It's easier to rewrite the
code than simply try and patch it up.

This patch
- splits the ldisc from the tty (so we will be able to refcount it more cleanly
  later)
- introduces a mutex lock for ldisc changing on an active device
- fixes the complete mess that hangup caused
- implements hopefully correct setldisc/close/hangup locking

There are still some problems around pty pairs that have always been there but
at least it is now possible to understand the code and fix further problems.

This fixes the following known bugs
- hang up can leak ldisc references
- hang up may not call open/close on ldisc in a matched way
- pty/tty pairs can deadlock during an ldisc change
- reading the ldisc proc files can cause every ldisc to be loaded

and probably a few other of the mysterious ldisc race reports.

I'm sure it also adds the odd new one.

Signed-off-by: default avatarAlan Cox <alan@linux.intel.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e8b70e7d

drivers/bluetooth/hci_ldisc.c

+2 −2
Original line number Diff line number Diff line
@@ -277,8 +277,8 @@ static int hci_uart_tty_open(struct tty_struct *tty) 
	/* FIXME: why is this needed. Note don't use ldisc_ref here as the

	   open path is before the ldisc is referencable */



	if (tty->ldisc.ops->flush_buffer)

		tty->ldisc.ops->flush_buffer(tty);

	if (tty->ldisc->ops->flush_buffer)

		tty->ldisc->ops->flush_buffer(tty);

	tty_driver_flush_buffer(tty);



	return 0;

drivers/char/cyclades.c

+1 −1
Original line number Diff line number Diff line
@@ -5200,7 +5200,7 @@ static int cyclades_proc_show(struct seq_file *m, void *v) 
					(cur_jifs - info->idle_stats.recv_idle)/

					HZ, info->idle_stats.overruns,

					/* FIXME: double check locking */

					(long)info->port.tty->ldisc.ops->num);

					(long)info->port.tty->ldisc->ops->num);

			else

				seq_printf(m, "%3d %8lu %10lu %8lu "

					"%10lu %8lu %9lu %6ld\n",

drivers/char/epca.c

+2 −2
Original line number Diff line number Diff line
@@ -2114,8 +2114,8 @@ static int pc_ioctl(struct tty_struct *tty, struct file *file, 
			tty_wait_until_sent(tty, 0);

		} else {

			/* ldisc lock already held in ioctl */

			if (tty->ldisc.ops->flush_buffer)

				tty->ldisc.ops->flush_buffer(tty);

			if (tty->ldisc->ops->flush_buffer)

				tty->ldisc->ops->flush_buffer(tty);

		}

		unlock_kernel();

		/* Fall Thru */

drivers/char/ip2/i2lib.c

+2 −2
Original line number Diff line number Diff line
@@ -868,11 +868,11 @@ i2Input(i2ChanStrPtr pCh) 
		amountToMove = count;

	}

	// Move the first block

	pCh->pTTY->ldisc.ops->receive_buf( pCh->pTTY,

	pCh->pTTY->ldisc->ops->receive_buf( pCh->pTTY,

		 &(pCh->Ibuf[stripIndex]), NULL, amountToMove );

	// If we needed to wrap, do the second data move

	if (count > amountToMove) {

		pCh->pTTY->ldisc.ops->receive_buf( pCh->pTTY,

		pCh->pTTY->ldisc->ops->receive_buf( pCh->pTTY,

		 pCh->Ibuf, NULL, count - amountToMove );

	}

	// Bump and wrap the stripIndex all at once by the amount of data read. This

drivers/char/ip2/ip2main.c

+2 −2
Original line number Diff line number Diff line
@@ -1315,8 +1315,8 @@ static inline void isig(int sig, struct tty_struct *tty, int flush) 
	if (tty->pgrp)

		kill_pgrp(tty->pgrp, sig, 1);

	if (flush || !L_NOFLSH(tty)) {

		if ( tty->ldisc.ops->flush_buffer )  

			tty->ldisc.ops->flush_buffer(tty);

		if ( tty->ldisc->ops->flush_buffer )  

			tty->ldisc->ops->flush_buffer(tty);

		i2InputFlush( tty->driver_data );

	}

}

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