devpts operations are protected by inode mutexes and dentry
refcounting. There is no need to hold BTM.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

The code looks like:
if (tty->driver->subtype == PTY_TYPE_MASTER) {
  ...
  if (tty->driver == ptm_driver)

But the second if is superfluous because only the ptm_driver is of
PTY_TYPE_MASTER subtype.

Also we can remove the #if now because devpts_pty_kill is defined as
an empty function for non-CONFIG_UNIX98_PTYS configs.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Acked-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Let's move this stuff to the better place, where we can account pty right in
tty-indexes managing code.
Signed-off-by: NKonstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

cleanup hack added in v2.6.27-3203-g15582d36

comment from that patch:

: pty: If the administrator creates a device for a ptmx slave we should not error
:
: The open path for ptmx slaves is via the ptmx device. Opening them any
: other way is not allowed. Vegard Nossum found that previously this was not
: the case and mknod foo c 128 42; cat foo would produce nasty diagnostics
:
: Signed-off-by: Alan Cox <alan@redhat.com>
: Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

devpts_get_tty() returns non-null only for inodes on devpts, but there is no
inodes for master-devices, /dev/ptmx (/dev/pts/ptmx) is the only way to open them.
Thus we can completely forbid lookup for master-devices and eliminate that hack in
tty_init_dev() because tty_open() will get EIO from tty_driver_lookup_tty().
Signed-off-by: NKonstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

Instead of the hackish way of counting ptys, let's define a specific
->remove hook both from slave and master. And decrease the count only
for master.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

Mistakenly, commit 64ba3dc3 (tty: never hold BTM while getting
tty_mutex) switched one fail path in ptmx_open to not free the newly
allocated tty.

Fix that by jumping to the appropriate place. And rename the labels so
that it's clear what is going on there.

Introduced-in: v2.6.36-rc2
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Cc: stable <stable@vger.kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

If tty_add_file fails at the point it is now, we have to revert all
the changes we did to the tty. It means either decrease all refcounts
if this was a tty reopen or delete the tty if it was newly allocated.

There was a try to fix this in v3.0-rc2 using tty_release in 0259894c
(TTY: fix fail path in tty_open). But instead it introduced a NULL
dereference. It's because tty_release dereferences
filp->private_data, but that one is set even in our tty_add_file. And
when tty_add_file fails, it's still NULL/garbage. Hence tty_release
cannot be called there.

To circumvent the original leak (and the current NULL deref) we split
tty_add_file into two functions, making the latter non-failing. In
that case we may do the former early in open, where handling failures
is easy. The latter stays as it is now. So there is no change in
functionality.

The original bug (leak) was introduced by f573bd17 (tty: Remove
__GFP_NOFAIL from tty_add_file()). Thanks Dan for reporting this.

Later, we may split tty_release into more functions and call only some
of them in this fail path instead. (If at all possible.)

Introduced-in: v2.6.37-rc2
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Cc: stable <stable@vger.kernel.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

tty_operations->remove is normally called like:
queue_release_one_tty
 ->tty_shutdown
   ->tty_driver_remove_tty
     ->tty_operations->remove

However tty_shutdown() is called from queue_release_one_tty() only if
tty_operations->shutdown is NULL. But for pty, it is not.
pty_unix98_shutdown() is used there as ->shutdown.

So tty_operations->remove of pty (i.e. pty_unix98_remove()) is never
called. This results in invalid pty_count. I.e. what can be seen in
/proc/sys/kernel/pty/nr.

I see this was already reported at:
  https://lkml.org/lkml/2009/11/5/370
But it was not fixed since then.

This patch is kind of a hackish way. The problem lies in ->install. We
allocate there another tty (so-called tty->link). So ->install is
called once, but ->remove twice, for both tty and tty->link. The fix
here is to count both tty and tty->link and divide the count by 2 for
user.

And to have ->remove called, let's make tty_driver_remove_tty() global
and call that from pty_unix98_shutdown() (tty_operations->shutdown).

While at it, let's document that when ->shutdown is defined,
tty_shutdown() is not called.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: stable <stable@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

remove invalid location line in each file header after location
moved from driver/char to driver/tty
Signed-off-by: NJovi Zhang <bookjovi@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

Used the newly introduced deinitialize_tty_struct to properly shut
down ldisc.

It is intended to fix the Julian's reported problem. He reports that
kmemleak checker warns about memory leak:
unreferenced object 0xc0e19860 (size 8):
comm cat, pid 1226, jiffies 4294919464 (age 287.476s)
hex dump (first 8 bytes):
44 de 2d c1 01 00 00 00 D.-.....
backtrace:
[<c1065a74>] create_object+0x109/0x1ad
[<c1063d2b>] kmem_cache_alloc+0x60/0x68
[<c113505c>] tty_ldisc_get+0x54/0x76
[<c11358c9>] tty_ldisc_init+0xa/0x20
[<c1130ab4>] initialize_tty_struct+0x2d/0x1ac
[<c1130c8c>] tty_init_dev+0x59/0x10d
[<c113136d>] tty_open+0x24a/0x3a2
...
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Reported-by: NJulian Anastasov <ja@ssi.bg>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

Change it so that we call the deinit functions at one place at the end
of the function (by gotos). And while at it use some sane label names.

This is a preparation for the deinitialization of tty in the next
patch.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Julian Anastasov <ja@ssi.bg>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

Change it so that we call the deinit functions at one place at the end
of the function (by gotos). And while at it use some sane label names.

This is a preparation for the deinitialization of tty in the next
patch.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Julian Anastasov <ja@ssi.bg>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

These were missed the last time I cleaned this up
globally, because of code moving around or new code
getting merged.
Signed-off-by: NArnd Bergmann <arnd@arndb.de>

Only oddities here are a couple of drivers that bogusly called the ldisc
helpers instead of returning -ENOIOCTLCMD. Fix the bug and the rest goes
away.
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

The tty code should be in its own subdirectory and not in the char
driver with all of the cruft that is currently there.

Based on work done by Arnd Bergmann <arnd@arndb.de>
Acked-by: NArnd Bergmann <arnd@arndb.de>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

This patch removes __GFP_NOFAIL use from tty_add_file() and adds proper error
handling to the call-sites of the function.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: NPekka Enberg <penberg@kernel.org>
Acked-by: NDavid Rientjes <rientjes@google.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

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 <hch@infradead.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: NNick Piggin <npiggin@kernel.dk>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

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 <hch@infradead.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Acked-by: NAndi Kleen <ak@linux.intel.com>
Acked-by: NGreg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: NNick Piggin <npiggin@kernel.dk>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

When the console has been redirected, a hangup of the tty
will cause tty_release to be called under the big tty_mutex,
which leads to a deadlock because hangup is also called
under the BTM.

This moves the BTM deeper into the tty_hangup function so
we can close the redirected tty without holding the BTM.
In case of pty, we now need to drop the BTM before
calling tty_vhangup.
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Acked-by: NAlan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: John Kacur <jkacur@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

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: NArnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

tty_mutex is never taken with the BTM held, except for
two corner cases that are worked around here.
We give up the BTM before calling tty_release() in the
error path of tty_open().
Similarly, we reorder the locking in ptmx_open()
to get tty_mutex before the BTM.
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

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: NArnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

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=17741Signed-off-by: NHoward Chu <hyc@symas.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h

percpu.h is included by sched.h and module.h and thus ends up being
included when building most .c files.  percpu.h includes slab.h which
in turn includes gfp.h making everything defined by the two files
universally available and complicating inclusion dependencies.

percpu.h -> slab.h dependency is about to be removed.  Prepare for
this change by updating users of gfp and slab facilities include those
headers directly instead of assuming availability.  As this conversion
needs to touch large number of source files, the following script is
used as the basis of conversion.

  http://userweb.kernel.org/~tj/misc/slabh-sweep.py

The script does the followings.

* Scan files for gfp and slab usages and update includes such that
  only the necessary includes are there.  ie. if only gfp is used,
  gfp.h, if slab is used, slab.h.

* When the script inserts a new include, it looks at the include
  blocks and try to put the new include such that its order conforms
  to its surrounding.  It's put in the include block which contains
  core kernel includes, in the same order that the rest are ordered -
  alphabetical, Christmas tree, rev-Xmas-tree or at the end if there
  doesn't seem to be any matching order.

* If the script can't find a place to put a new include (mostly
  because the file doesn't have fitting include block), it prints out
  an error message indicating which .h file needs to be added to the
  file.

The conversion was done in the following steps.

1. The initial automatic conversion of all .c files updated slightly
   over 4000 files, deleting around 700 includes and adding ~480 gfp.h
   and ~3000 slab.h inclusions.  The script emitted errors for ~400
   files.

2. Each error was manually checked.  Some didn't need the inclusion,
   some needed manual addition while adding it to implementation .h or
   embedding .c file was more appropriate for others.  This step added
   inclusions to around 150 files.

3. The script was run again and the output was compared to the edits
   from #2 to make sure no file was left behind.

4. Several build tests were done and a couple of problems were fixed.
   e.g. lib/decompress_*.c used malloc/free() wrappers around slab
   APIs requiring slab.h to be added manually.

5. The script was run on all .h files but without automatically
   editing them as sprinkling gfp.h and slab.h inclusions around .h
   files could easily lead to inclusion dependency hell.  Most gfp.h
   inclusion directives were ignored as stuff from gfp.h was usually
   wildly available and often used in preprocessor macros.  Each
   slab.h inclusion directive was examined and added manually as
   necessary.

6. percpu.h was updated not to include slab.h.

7. Build test were done on the following configurations and failures
   were fixed.  CONFIG_GCOV_KERNEL was turned off for all tests (as my
   distributed build env didn't work with gcov compiles) and a few
   more options had to be turned off depending on archs to make things
   build (like ipr on powerpc/64 which failed due to missing writeq).

   * x86 and x86_64 UP and SMP allmodconfig and a custom test config.
   * powerpc and powerpc64 SMP allmodconfig
   * sparc and sparc64 SMP allmodconfig
   * ia64 SMP allmodconfig
   * s390 SMP allmodconfig
   * alpha SMP allmodconfig
   * um on x86_64 SMP allmodconfig

8. percpu.h modifications were reverted so that it could be applied as
   a separate patch and serve as bisection point.

Given the fact that I had only a couple of failures from tests on step
6, I'm fairly confident about the coverage of this conversion patch.
If there is a breakage, it's likely to be something in one of the arch
headers which should be easily discoverable easily on most builds of
the specific arch.
Signed-off-by: NTejun Heo <tj@kernel.org>
Guess-its-ok-by: NChristoph Lameter <cl@linux-foundation.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>

In particular, several occurances of funny versions of 'success',
'unknown', 'therefore', 'acknowledge', 'argument', 'achieve', 'address',
'beginning', 'desirable', 'separate' and 'necessary' are fixed.
Signed-off-by: NDaniel Mack <daniel@caiaq.de>
Cc: Joe Perches <joe@perches.com>
Cc: Junio C Hamano <gitster@pobox.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

Start trying to untangle the remaining BKL mess

Updated to fix missing unlock_kernel noted by Dan Carpenter
Signed-off-by: NAlan "I must be out of my tree" Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

For consistency drop & in front of every proc_handler.  Explicity
taking the address is unnecessary and it prevents optimizations
like stubbing the proc_handlers to NULL.

Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: NEric W. Biederman <ebiederm@xmission.com>

Now that sys_sysctl is a wrapper around /proc/sys all of
the binary sysctl support elsewhere in the tree is
dead code.

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Corey Minyard <minyard@acm.org>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Neil Brown <neilb@suse.de>
Cc: "James E.J. Bottomley" <James.Bottomley@suse.de>
Acked-by: Clemens Ladisch <clemens@ladisch.de> for drivers/char/hpet.c
Signed-off-by: NEric W. Biederman <ebiederm@xmission.com>

After m68k's task_thread_info() doesn't refer to current,
it's possible to remove sched.h from interrupt.h and not break m68k!
Many thanks to Heiko Carstens for allowing this.
Signed-off-by: NAlexey Dobriyan <adobriyan@gmail.com>

David Howells noticed (due to the compiler warning about an unused
'pty_ops_bsd' variable) that we haven't actually been using the code
that implements TIOCSPTLCK for legacy pty handling.  It's been that way
since 2.6.26, commit 3e8e88ca to be
exact ("pty: prepare for tty->ops changes").

DavidH initially submitted a patch just removing the dead code entirely,
and since nobody has apparently ever complained, I'm not entirely sure
that wouldn't be the right thing to do.  But since the whole and only
point of the legacy pty code is to be compatible with legacy distros
that don't use the new unix98 pty model, let's just wire it up again.

And clean it up a bit while we're at it.
Acked-by: NDavid Howells <dhowells@redhat.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Commit ac89a917 ("pty: don't limit the writes to 'pty_space()' inside
'pty_write()'") removed the pty_space() checking, in order to let the
regular tty buffer code limit the buffering itself.

That was all good, but as a subtle side effect it meant that we'd be
doing a tty_wakeup() even in the case where the buffers were all filled
up, and didn't actually make any progress on the write.

Which sounds innocuous, but it interacts very badly with the ppp_async
code, which has an infinite loop in ppp_async_push() that tries to push
out data to the tty.  When we call tty_wakeup(), that loop ends up
thinking that progress was made (see the subtle interactions between
XMIT_WAKEUP and 'tty_stuffed' for details).  End result: one unhappy ppp
user.

Fixed by noticing when tty_insert_flip_string() didn't actually do
anything, and then not doing any more processing (including, very much
not calling tty_wakeup()).
Bisected-and-tested-by: NPeter Volkov <pva@gentoo.org>
Cc: stable@kernel.org (2.6.31)
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The whole write-room thing is something that is up to the _caller_ to
worry about, not the pty layer itself.  The total buffer space will
still be limited by the buffering routines themselves, so there is no
advantage or need in having pty_write() artificially limit the size
somehow.

And what happened was that the caller (the n_tty line discipline, in
this case) may have verified that there is room for 2 bytes to be
written (for NL -> CRNL expansion), and it used to then do those writes
as two single-byte writes.  And if the first byte written (CR) then
caused a new tty buffer to be allocated, pty_space() may have returned
zero when trying to write the second byte (LF), and then incorrectly
failed the write - leading to a lost newline character.

This should finally fix

	http://bugzilla.kernel.org/show_bug.cgi?id=14015Reported-by: NMikael Pettersson <mikpe@it.uu.se>
Acked-by: NAlan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Commit d945cb9c ("pty: Rework the pty layer to use the normal buffering
logic") dropped the test for 'tty->stopped' in pty_write_room(), which
then causes the n_tty line discipline thing to not throttle the data
properly when the tty is stopped.

So instead of pausing the write due to the tty being stopped, the ldisc
layer would go ahead and push it down to the pty.  The pty write()
routine would then refuse to take the data (because it _did_ check
'stopped'), and the data wouldn't actually be written.

This whole stopped test should eventually be moved into the tty ldisc
layer rather than have low-level tty drivers care about these things,
but right now the fix is to just re-instate the missing pty 'stopped'
handling.
Reported-and-tested-by: NArtur Skawina <art.08.09@gmail.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

We really don't want to mark the pty as a low-latency device, because as
Alan points out, the ->write method can be called from an IRQ (ppp?),
and that means we can't use ->low_latency=1 as we take mutexes in the
low_latency case.

So rather than using low_latency to force the written data to be pushed
to the ldisc handling at 'write()' time, just make the reader side (or
the poll function) do the flush when it checks whether there is data to
be had.

This also fixes the problem with lost data in an emacs compile buffer
(bugzilla 13815), and we can thus revert the low_latency pty hack
(commit 3a542974: "pty: quickfix for the
pty ENXIO timing problems").
Signed-off-by: NOGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Tested-by: NAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
[ Modified to do the tty_flush_to_ldisc() inside input_available_p() so
  that it triggers for both read and poll()  - Linus]
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This also makes close stall in the normal case which is apparently
needed to fix emacs
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

* Remove smp_lock.h from files which don't need it (including some headers!)
* Add smp_lock.h to files which do need it
* Make smp_lock.h include conditional in hardirq.h
  It's needed only for one kernel_locked() usage which is under CONFIG_PREEMPT

  This will make hardirq.h inclusion cheaper for every PREEMPT=n config
  (which includes allmodconfig/allyesconfig, BTW)
Signed-off-by: NAlexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This fixes the ppp problems and various other issues with call locking
caused by one side of a pty called in one locking context trying to match
another with differing rules on the other side. We also get a big slack
space to work with that means we can bury the flow control deadlock case
for any conceivable real world situation.
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The pty code has always been buggy on its ldisc handling. The recent
changes made the window for the race much bigger. Pending fixing it
properly which is not at all trivial, at least make the race small again so
we don't disrupt other dev work.
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The pty code has always been buggy on its ldisc handling. The recent
changes made the window for the race much bigger. Pending fixing it
properly which is not at all trivial, at least make the race small again so
we don't disrupt other dev work.
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

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: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>