linux-toradex.git/include/linux/tty.h, branch tegra-10.11.4

TTY: open/hangup race fixup

2010-12-09T21:32:42+00:00

commit acfa747baf73922021a047f2d87a2d866f5dbab5 upstream.

Like in the "TTY: don't allow reopen when ldisc is changing" patch,
this one fixes a TTY WARNING as described in the option 1) there:
1) __tty_hangup from tty_ldisc_hangup to tty_ldisc_enable. During this
section tty_lock is held. However tty_lock is temporarily dropped in
the middle of the function by tty_ldisc_hangup.

The fix is to introduce a new flag which we set during the unlocked
window and check it in tty_reopen too. The flag is TTY_HUPPING and is
cleared after TTY_HUPPED is set.

While at it, remove duplicate TTY_HUPPED set_bit. The one after
calling ops->hangup seems to be more correct. But anyway, we hold
tty_lock, so there should be no difference.

Also document the function it does that kind of crap.

Nicely reproducible with two forked children:
static void do_work(const char *tty)
{
	if (signal(SIGHUP, SIG_IGN) == SIG_ERR) exit(1);
	setsid();
	while (1) {
		int fd = open(tty, O_RDWR|O_NOCTTY);
		if (fd < 0) continue;
		if (ioctl(fd, TIOCSCTTY)) continue;
		if (vhangup()) continue;
		close(fd);
	}
	exit(0);
}

Signed-off-by: Jiri Slaby 
Reported-by: 
Reported-by: Kyle McMartin 
Cc: Alan Cox 
Signed-off-by: Greg Kroah-Hartman

tty: fix fu_list abuse

2010-08-18T12:35:47+00:00

tty: fix fu_list abuse

tty code abuses fu_list, which causes a bug in remount,ro handling.

If a tty device node is opened on a filesystem, then the last link to the inode
removed, the filesystem will be allowed to be remounted readonly. This is
because fs_may_remount_ro does not find the 0 link tty inode on the file sb
list (because the tty code incorrectly removed it to use for its own purpose).
This can result in a filesystem with errors after it is marked "clean".

Taking idea from Christoph's initial patch, allocate a tty private struct
at file->private_data and put our required list fields in there, linking
file and tty. This makes tty nodes behave the same way as other device nodes
and avoid meddling with the vfs, and avoids this bug.

The error handling is not trivial in the tty code, so for this bugfix, I take
the simple approach of using __GFP_NOFAIL and don't worry about memory errors.
This is not a problem because our allocator doesn't fail small allocs as a rule
anyway. So proper error handling is left as an exercise for tty hackers.

[ Arguably filesystem's device inode would ideally be divorced from the
driver's pseudo inode when it is opened, but in practice it's not clear whether
that will ever be worth implementing. ]

Cc: linux-kernel@vger.kernel.org
Cc: Christoph Hellwig 
Cc: Alan Cox 
Cc: Greg Kroah-Hartman 
Signed-off-by: Nick Piggin 
Signed-off-by: Al Viro

fs: cleanup files_lock locking

2010-08-18T12:35:47+00:00

fs: cleanup files_lock locking

Lock tty_files with a new spinlock, tty_files_lock; provide helpers to
manipulate the per-sb files list; unexport the files_lock spinlock.

Cc: linux-kernel@vger.kernel.org
Cc: Christoph Hellwig 
Cc: Alan Cox 
Acked-by: Andi Kleen 
Acked-by: Greg Kroah-Hartman 
Signed-off-by: Nick Piggin 
Signed-off-by: Al Viro

tty: implement BTM as mutex instead of BKL

2010-08-10T20:47:44+00:00

The tty locking now follows the rules for mutexes, so
we can replace the BKL usage with a new subsystem
wide mutex.

Using a regular mutex here will change the behaviour
when blocked on the BTM from spinning to sleeping,
but that should not be visible to the user.

Using the mutex also means that all the BTM is now
covered by lockdep.

Signed-off-by: Arnd Bergmann 
Cc: Alan Cox 
Signed-off-by: Greg Kroah-Hartman

tty: remove tty_lock_nested

2010-08-10T20:47:44+00:00

This changes all remaining users of tty_lock_nested
to be non-recursive, which lets us kill this function.
As a consequence, we won't need to keep the lock count
any more, which allows more simplifications later.

Signed-off-by: Arnd Bergmann 
Cc: Alan Cox 
Signed-off-by: Greg Kroah-Hartman

tty: introduce wait_event_interruptible_tty

2010-08-10T20:47:43+00:00

Calling wait_event_interruptible implicitly
releases the BKL when it sleeps, but we need
to do this explcitly when we have converted
it to a mutex.

Signed-off-by: Arnd Bergmann 
Cc: Alan Cox 
Signed-off-by: Greg Kroah-Hartman

tty: replace BKL with a new tty_lock

2010-08-10T20:47:43+00:00

As a preparation for replacing the big kernel lock
in the TTY layer, wrap all the callers in new
macros tty_lock, tty_lock_nested and tty_unlock.

Signed-off-by: Arnd Bergmann 
Cc: Alan Cox 
Signed-off-by: Greg Kroah-Hartman

tty: Add EXTPROC support for LINEMODE

2010-08-10T20:47:39+00:00

This patch is against the 2.6.34 source.

Paraphrased from the 1989 BSD patch by David Borman @ cray.com:

     These are the changes needed for the kernel to support
     LINEMODE in the server.

     There is a new bit in the termios local flag word, EXTPROC.
     When this bit is set, several aspects of the terminal driver
     are disabled.  Input line editing, character echo, and mapping
     of signals are all disabled.  This allows the telnetd to turn
     off these functions when in linemode, but still keep track of
     what state the user wants the terminal to be in.

     New ioctl:
         TIOCSIG         Generate a signal to processes in the
                         current process group of the pty.

     There is a new mode for packet driver, the TIOCPKT_IOCTL bit.
     When packet mode is turned on in the pty, and the EXTPROC bit
     is set, then whenever the state of the pty is changed, the
     next read on the master side of the pty will have the TIOCPKT_IOCTL
     bit set.  This allows the process on the server side of the pty
     to know when the state of the terminal has changed; it can then
     issue the appropriate ioctl to retrieve the new state.

Since the original BSD patches accompanied the source code for telnet
I've left that reference here, but obviously the feature is useful for
any remote terminal protocol, including ssh.

The corresponding feature has existed in the BSD tty driver since 1989.
For historical reference, a good copy of the relevant files can be found
here:

http://anonsvn.mit.edu/viewvc/krb5/trunk/src/appl/telnet/?pathrev=17741

Signed-off-by: Howard Chu 
Cc: Alan Cox 
Signed-off-by: Greg Kroah-Hartman

Fix init ordering of /dev/console vs callers of modprobe

2010-08-06T16:17:02+00:00

Make /dev/console get initialised before any initialisation routine that
invokes modprobe because if modprobe fails, it's going to want to open
/dev/console, presumably to write an error message to.

The problem with that is that if the /dev/console driver is not yet
initialised, the chardev handler will call request_module() to invoke
modprobe, which will fail, because we never compile /dev/console as a
module.

This will lead to a modprobe loop, showing the following in the kernel
log:

	request_module: runaway loop modprobe char-major-5-1
	request_module: runaway loop modprobe char-major-5-1
	request_module: runaway loop modprobe char-major-5-1
	request_module: runaway loop modprobe char-major-5-1
	request_module: runaway loop modprobe char-major-5-1

This can happen, for example, when the built in md5 module can't find
the built in cryptomgr module (because the latter fails to initialise).
The md5 module comes before the call to tty_init(), presumably because
'crypto' comes before 'drivers' alphabetically.

Fix this by calling tty_init() from chrdev_init().

Signed-off-by: David Howells 
Signed-off-by: Linus Torvalds

tty: n_gsm line discipline

2010-05-21T16:34:29+00:00

Add an implementation of GSM 0710 MUX. The implementation currently supports

- Basic and advanced framing (as either end of the link)
- UI or UIH data frames
- Adaption layer 1-4 (1 and 2 via tty, 3 and 4 as skbuff lists)
- Modem and control messages including the correct retry process
- Flow control

and exposes the MUX channels as a set of virtual tty devices including modem
signals. This is an experimental driver.

Signed-off-by: Alan Cox 
Signed-off-by: Greg Kroah-Hartman