Separate the head & commit indices from the tail index to avoid
cache-line contention (so called 'false-sharing') between concurrent
threads.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Since neither echo_commit nor echo_tail can change for the duration
of __process_echoes loop, substitute index comparison for the
snapshot counter.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Don't have the driver flush received echoes if no echoes were
actually output.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Byte-by-byte echo output is painfully slow, requiring a lock/unlock
cycle for every input byte.

Instead, perform the echo output in blocks of 256 characters, and
at least once per flip buffer receive. Enough space is reserved in
the echo buffer to guarantee a full block can be saved without
overrunning the echo output. Overrun is prevented by discarding
the oldest echoes until enough space exists in the echo buffer
to receive at least a full block of new echoes.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Use output_lock mutex as a memory barrier when storing echo_commit.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Adding data to echo_buf (via add_echo_byte()) is guaranteed to be
single-threaded, since all callers are from the n_tty_receive_buf()
path. Processing the echo_buf can be called from either the
n_tty_receive_buf() path or the n_tty_write() path; however, these
callers are already serialized by output_lock.

Publish cumulative echo_head changes to echo_commit; process echo_buf
from echo_tail to echo_commit; remove echo_lock.

On echo_buf overrun, claim output_lock to serialize changes to
echo_tail.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Prepare for lockless echo_buf handling; compute current byte count
of echo_buf from head and tail indices.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Instead of using a single index to track the current echo_buf position,
use a head index when adding to the buffer and a tail index when
consuming from the buffer. Allow these head and tail indices to wrap
at max representable value; perform modulo reduction via helper
functions when accessing the buffer.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

The echo_overrun field is only assigned and never tested; remove it.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Scheduling buffer work on the same cpu as the read() thread
limits the parallelism now possible between the receive_buf path
and the n_tty_read() path.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

The pty driver forces ldisc flow control on, regardless of available
receive buffer space, so the writer can be woken whenever unthrottle
is called. However, this 'forced throttle' has performance
consequences, as multiple atomic operations are necessary to
unthrottle and perform the write wakeup for every input line (in
canonical mode).

Instead, short-circuit the unthrottle if the tty is a pty and perform
the write wakeup directly.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Prepare to special case pty flow control; avoid forward declaration.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Prepare for special handling of pty throttle/unthrottle; factor
flow control into helper functions.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Prepare to factor throttle and unthrottle into helper functions;
relocate chars_in_buffer() to avoid forward declaration.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

No tty driver modifies termios during throttle() or unthrottle().
Therefore, only read safety is required.

However, tty_throttle_safe and tty_unthrottle_safe must still be
mutually exclusive; introduce throttle_mutex for that purpose.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

If the read buffer indices are in the same cache-line, cpus will
contended over the cache-line (so called 'false sharing').

Separate the producer-published fields from the consumer-published
fields; document the locks relevant to each field.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

User-space read() can run concurrently with receiving from device;
waiting for receive_buf() to complete is not required.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

lnext escapes the next input character as a literal, and must
be reset when canonical mode changes (to avoid misinterpreting
a special character as a literal if canonical mode is changed
back again).

lnext is specifically not reset on a buffer flush so as to avoid
misinterpreting the next input character as a special character.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

n_tty has a single-producer/single-consumer input model;
use lockless publish instead.

Use termios_rwsem to exclude both consumer and producer while
changing or resetting buffer indices, eg., when flushing. Also,
claim exclusive termios_rwsem to safely retrieve the buffer
indices from a thread other than consumer or producer
(eg., TIOCINQ ioctl).

Note the read_tail is published _after_ clearing the newline
indicator in read_flags to avoid racing the producer.

Drop read_lock spinlock.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

canon_data represented the # of lines which had been copied
to the receive buffer but not yet copied to the user buffer.
The value was tested to determine if input was available in
canonical mode (and also to force input overrun if the
receive buffer was full but a newline had not been received).

However, the actual count was irrelevent; only whether it was
non-zero (meaning 'is there any input to transfer?'). This
shared count is unnecessary and unsafe with a lockless algorithm.
The same check is made by comparing canon_head with read_tail instead.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Use termios_rwsem to guarantee safe access to the termios values.
This is particularly important for N_TTY as changing certain termios
settings alters the mode of operation.

termios_rwsem must be dropped across throttle/unthrottle since
those functions claim the termios_rwsem exclusively (to guarantee
safe access to the termios and for mutual exclusion).
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

termios is commonly accessed unsafely (especially by N_TTY)
because the existing mutex forces exclusive access.
Convert existing usage.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Storing the read_cnt creates an unnecessary shared variable
between the single-producer (n_tty_receive_buf()) and the
single-consumer (n_tty_read()).

Compute read_cnt from head & tail instead of storing.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Wrap read_buf indices (read_head, read_tail, canon_head) at
max representable value, instead of at the N_TTY_BUF_SIZE. This step
is necessary to allow lockless reads of these shared variables
(by updating the variables atomically).
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Prepare for replacing read_cnt field with computed value.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

N_TTY .chars_in_buffer() method requires serialized access if
the current thread is not the single-consumer, n_tty_read().

Separate the internal interface; prepare for lockless read-side.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Instead of pushing one char per loop, pre-compute the data length
to copy and copy all at once.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Simplify n_tty_read(); extract complex copy algorithm
into separate function, canon_copy_to_user().
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Although line discipline receiving is single-producer/single-consumer,
using tty->receive_room to manage flow control creates unnecessary
critical regions requiring additional lock use.

Instead, introduce the optional .receive_buf2() ldisc method which
returns the # of bytes actually received. Serialization is guaranteed
by the caller.

In turn, the line discipline should schedule the buffer work item
whenever space becomes available; ie., when there is room to receive
data and receive_room() previously returned 0 (the buffer work
item stops processing if receive_buf2() returns 0). Note the
'no room' state need not be atomic despite concurrent use by two
threads because only the buffer work thread can set the state and
only the read() thread can clear the state.

Add n_tty_receive_buf2() as the receive_buf2() method for N_TTY.
Provide a public helper function, tty_ldisc_receive_buf(), to use
when directly accessing the receive_buf() methods.

Line disciplines not using input flow control can continue to set
tty->receive_room to a fixed value and only provide the receive_buf()
method.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Although the driver-side input path must update the available
buffer space, it should not reschedule itself. If space is still
available and the flip buffers are not empty, flush_to_ldisc()
will loop again.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

receive_room is used to control the amount of data the flip
buffer work can push to the read buffer. This update is unsafe:

  CPU 0                        |  CPU 1
                               |
                               | n_tty_read()
                               |   n_tty_set_room()
                               |     left = <calc of space>
n_tty_receive_buf()            |
  <push data to buffer>        |
  n_tty_set_room()             |
    left = <calc of space>     |
    tty->receive_room = left   |
                               |     tty->receive_room = left

receive_room is now updated with a stale calculation of the
available buffer space, and the subsequent work loop will likely
overwrite unread data in the input buffer.

Update receive_room atomically with the calculation of the
available buffer space.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

minimum_to_wake is unique to N_TTY processing, and belongs in
per-ldisc data.

Add the ldisc method, ldisc_ops::fasync(), to notify line disciplines
when signal-driven I/O is enabled or disabled. When enabled for N_TTY
(by fcntl(F_SETFL, O_ASYNC)), blocking reader/polls will be woken
for any readable input. When disabled, blocking reader/polls are not
woken until the read buffer is full.

Canonical mode (L_ICANON(tty), n_tty_data::icanon) is not affected by
the minimum_to_wake setting.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

I meet emacs hang in start if I do the operation below:
  1: echo 3 > /proc/sys/vm/drop_caches
  2: emacs BigFile
  3: Press CTRL-S follow 2 immediately

Then emacs hang on, CTRL-Q can't resume, the terminal
hang on, you can do nothing with this terminal except
close it.

The reason is before emacs takeover control the tty,
we use CTRL-S to XOFF it. Then when emacs takeover the
control, it may don't use the flow-control, so emacs hang.
This patch fix it.

This patch will fix a kind of strange tty relation hang problem,
I believe I meet it with vim in ssh, and also see below bug report:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=465823Signed-off-by: NWang YanQing <udknight@gmail.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

No in-tree tty driver supports cooked mode in hardware; remove.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Buffer work may already be pending when the n_tty ldisc is re-opened,
eg., when setting the ldisc (via TIOCSETD ioctl) and when hanging up
the tty. Since n_tty_set_room() may restart buffer work, first ensure
the ldisc is completely initialized.

Factor n_tty_set_room() out of reset_buffer_flags() (only 2 callers)
and reorganize n_tty_open() to set termios last; buffer work will
be restarted there if necessary, after the char_map is properly
initialized.

Fixes this WARNING:

[  549.561769] ------------[ cut here ]------------
[  549.598755] WARNING: at drivers/tty/n_tty.c:160 n_tty_set_room+0xff/0x130()
[  549.604058] scheduling buffer work for halted ldisc
[  549.607741] Pid: 9417, comm: trinity-child28 Tainted: G      D W 3.7.0-next-20121217-sasha-00023-g8689ef9 #219
[  549.652580] Call Trace:
[  549.662754]  [<ffffffff81c432cf>] ? n_tty_set_room+0xff/0x130
[  549.665458]  [<ffffffff8110cae7>] warn_slowpath_common+0x87/0xb0
[  549.668257]  [<ffffffff8110cb71>] warn_slowpath_fmt+0x41/0x50
[  549.671007]  [<ffffffff81c432cf>] n_tty_set_room+0xff/0x130
[  549.673268]  [<ffffffff81c44597>] reset_buffer_flags+0x137/0x150
[  549.675607]  [<ffffffff81c45b71>] n_tty_open+0x131/0x1c0
[  549.677699]  [<ffffffff81c47824>] tty_ldisc_open.isra.5+0x54/0x70
[  549.680147]  [<ffffffff81c482bf>] tty_ldisc_hangup+0x11f/0x1e0
[  549.682409]  [<ffffffff81c3fa17>] __tty_hangup+0x137/0x440
[  549.684634]  [<ffffffff81c3fd49>] tty_vhangup+0x9/0x10
[  549.686443]  [<ffffffff81c4a42c>] pty_close+0x14c/0x160
[  549.688446]  [<ffffffff81c41225>] tty_release+0xd5/0x490
[  549.690460]  [<ffffffff8127d8a2>] __fput+0x122/0x250
[  549.692577]  [<ffffffff8127d9d9>] ____fput+0x9/0x10
[  549.694534]  [<ffffffff811348c2>] task_work_run+0xb2/0xf0
[  549.696349]  [<ffffffff81113c6d>] do_exit+0x36d/0x580
[  549.698286]  [<ffffffff8107d964>] ? syscall_trace_enter+0x24/0x2e0
[  549.702729]  [<ffffffff81113f4a>] do_group_exit+0x8a/0xc0
[  549.706775]  [<ffffffff81113f92>] sys_exit_group+0x12/0x20
[  549.711088]  [<ffffffff83cfab18>] tracesys+0xe1/0xe6
[  549.728001] ---[ end trace 73eb41728f11f87e ]---
Reported-by: NSasha Levin <levinsasha928@gmail.com>
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

The driver is no longer unthrottled on buffer reset, so remove
comments that claim it is.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

A buffer flush is both undesirable and unnecessary when the ldisc
is closing. A buffer flush performs the following:
 1. resets ldisc data fields to their initial state
 2. resets tty->receive_room to indicate more data can be sent
 3. schedules buffer work to receive more data
 4. signals a buffer flush has happened to linked pty in packet mode

Since the ldisc has been halted and the tty may soon be destructed,
buffer work must not be scheduled as that work might access
an invalid tty and ldisc state. Also, the ldisc read buffer is about
to be freed, so that's pointless.

Resetting the ldisc data fields is pointless as well since that
structure is about to be freed.

Resetting tty->receive_room is unnecessary, as it will be properly
reset if a new ldisc is reopened. Besides, resetting the original
receive_room value would be wrong since the read buffer will be
gone.

Since the packet mode flush is observable from userspace, this
behavior has been preserved.

The test jig originally authored by Ilya Zykov <ilya@ilyx.ru> and
signed off by him is included below. The test jig prompts the
following warnings which this patch fixes.

[   38.051111] ------------[ cut here ]------------
[   38.052113] WARNING: at drivers/tty/n_tty.c:160 n_tty_set_room.part.6+0x8b/0xa0()
[   38.053916] Hardware name: Bochs
[   38.054819] Modules linked in: netconsole configfs bnep rfcomm bluetooth parport_pc ppdev snd_hda_intel snd_hda_codec
snd_hwdep snd_pcm snd_seq_midi snd_rawmidi snd_seq_midi_event snd_seq psmouse snd_timer serio_raw mac_hid snd_seq_device
snd microcode lp parport virtio_balloon soundcore i2c_piix4 snd_page_alloc floppy 8139too 8139cp
[   38.059704] Pid: 1564, comm: pty_kill Tainted: G        W    3.7.0-next-20121130+ttydebug-xeon #20121130+ttydebug
[   38.061578] Call Trace:
[   38.062491]  [<ffffffff81058b4f>] warn_slowpath_common+0x7f/0xc0
[   38.063448]  [<ffffffff81058baa>] warn_slowpath_null+0x1a/0x20
[   38.064439]  [<ffffffff8142dc2b>] n_tty_set_room.part.6+0x8b/0xa0
[   38.065381]  [<ffffffff8142dc82>] n_tty_set_room+0x42/0x80
[   38.066323]  [<ffffffff8142e6f2>] reset_buffer_flags+0x102/0x160
[   38.077508]  [<ffffffff8142e76d>] n_tty_flush_buffer+0x1d/0x90
[   38.078782]  [<ffffffff81046569>] ? default_spin_lock_flags+0x9/0x10
[   38.079734]  [<ffffffff8142e804>] n_tty_close+0x24/0x60
[   38.080730]  [<ffffffff81431b61>] tty_ldisc_close.isra.2+0x41/0x60
[   38.081680]  [<ffffffff81431bbb>] tty_ldisc_kill+0x3b/0x80
[   38.082618]  [<ffffffff81432a07>] tty_ldisc_release+0x77/0xe0
[   38.083549]  [<ffffffff8142b781>] tty_release+0x451/0x4d0
[   38.084525]  [<ffffffff811950be>] __fput+0xae/0x230
[   38.085472]  [<ffffffff8119524e>] ____fput+0xe/0x10
[   38.086401]  [<ffffffff8107aa88>] task_work_run+0xc8/0xf0
[   38.087334]  [<ffffffff8105ea56>] do_exit+0x196/0x4b0
[   38.088304]  [<ffffffff8106c77b>] ? __dequeue_signal+0x6b/0xb0
[   38.089240]  [<ffffffff8105ef34>] do_group_exit+0x44/0xa0
[   38.090182]  [<ffffffff8106f43d>] get_signal_to_deliver+0x20d/0x4e0
[   38.091125]  [<ffffffff81016979>] do_signal+0x29/0x130
[   38.092096]  [<ffffffff81431a9e>] ? tty_ldisc_deref+0xe/0x10
[   38.093030]  [<ffffffff8142a317>] ? tty_write+0xb7/0xf0
[   38.093976]  [<ffffffff81193f53>] ? vfs_write+0xb3/0x180
[   38.094904]  [<ffffffff81016b20>] do_notify_resume+0x80/0xc0
[   38.095830]  [<ffffffff81700492>] int_signal+0x12/0x17
[   38.096788] ---[ end trace 5f6f7a9651cd999b ]---

[ 2730.570602] ------------[ cut here ]------------
[ 2730.572130] WARNING: at drivers/tty/n_tty.c:160 n_tty_set_room+0x107/0x140()
[ 2730.574904] scheduling buffer work for halted ldisc
[ 2730.578303] Pid: 9691, comm: trinity-child15 Tainted: G        W 3.7.0-rc8-next-20121205-sasha-00023-g59f0d85 #207
[ 2730.588694] Call Trace:
[ 2730.590486]  [<ffffffff81c41d77>] ? n_tty_set_room+0x107/0x140
[ 2730.592559]  [<ffffffff8110c827>] warn_slowpath_common+0x87/0xb0
[ 2730.595317]  [<ffffffff8110c8b1>] warn_slowpath_fmt+0x41/0x50
[ 2730.599186]  [<ffffffff81c41d77>] n_tty_set_room+0x107/0x140
[ 2730.603141]  [<ffffffff81c42fe7>] reset_buffer_flags+0x137/0x150
[ 2730.607166]  [<ffffffff81c43018>] n_tty_flush_buffer+0x18/0x90
[ 2730.610123]  [<ffffffff81c430af>] n_tty_close+0x1f/0x60
[ 2730.612068]  [<ffffffff81c461f2>] tty_ldisc_close.isra.4+0x52/0x60
[ 2730.614078]  [<ffffffff81c462ab>] tty_ldisc_reinit+0x3b/0x70
[ 2730.615891]  [<ffffffff81c46db2>] tty_ldisc_hangup+0x102/0x1e0
[ 2730.617780]  [<ffffffff81c3e537>] __tty_hangup+0x137/0x440
[ 2730.619547]  [<ffffffff81c3e869>] tty_vhangup+0x9/0x10
[ 2730.621266]  [<ffffffff81c48f1c>] pty_close+0x14c/0x160
[ 2730.622952]  [<ffffffff81c3fd45>] tty_release+0xd5/0x490
[ 2730.624674]  [<ffffffff8127fbe2>] __fput+0x122/0x250
[ 2730.626195]  [<ffffffff8127fd19>] ____fput+0x9/0x10
[ 2730.627758]  [<ffffffff81134602>] task_work_run+0xb2/0xf0
[ 2730.629491]  [<ffffffff811139ad>] do_exit+0x36d/0x580
[ 2730.631159]  [<ffffffff81113c8a>] do_group_exit+0x8a/0xc0
[ 2730.632819]  [<ffffffff81127351>] get_signal_to_deliver+0x501/0x5b0
[ 2730.634758]  [<ffffffff8106de34>] do_signal+0x24/0x100
[ 2730.636412]  [<ffffffff81204865>] ? user_exit+0xa5/0xd0
[ 2730.638078]  [<ffffffff81183cd8>] ? trace_hardirqs_on_caller+0x118/0x140
[ 2730.640279]  [<ffffffff81183d0d>] ? trace_hardirqs_on+0xd/0x10
[ 2730.642164]  [<ffffffff8106df78>] do_notify_resume+0x48/0xa0
[ 2730.643966]  [<ffffffff83cdff6a>] int_signal+0x12/0x17
[ 2730.645672] ---[ end trace a40d53149c07fce0 ]---

/*
 * pty_thrash.c
 *
 * Based on original test jig by Ilya Zykov <ilya@ilyx.ru>
 *
 * Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
 * Signed-off-by: Ilya Zykov <ilya@ilyx.ru>
 */

static int fd;

static void error_exit(char *f, ...)
{
        va_list va;

        va_start(va, f);
        vprintf(f, va);
        printf(": %s\n", strerror(errno));
        va_end(va);

        if (fd >= 0)
                close(fd);

        exit(EXIT_FAILURE);
}

int main(int argc, char *argv[]) {
        int parent;
        char pts_name[24];
        int ptn, unlock;

        while (1) {

                fd = open("/dev/ptmx", O_RDWR);
                if (fd < 0)
                        error_exit("opening pty master");
                unlock = 0;
                if (ioctl(fd, TIOCSPTLCK, &unlock) < 0)
                        error_exit("unlocking pty pair");
                if (ioctl(fd, TIOCGPTN, &ptn) < 0)
                        error_exit("getting pty #");
                snprintf(pts_name, sizeof(pts_name), "/dev/pts/%d", ptn);

                child_id = fork();
                if (child_id == -1)
                        error_exit("forking child");

                if (parent) {
                        int err, id, status;
                        char buf[128];
                        int n;

                        n = read(fd, buf, sizeof(buf));
                        if (n < 0)
                                error_exit("master reading");
                        printf("%.*s\n", n-1, buf);

                        close(fd);

                        err = kill(child_id, SIGKILL);
                        if (err < 0)
                                error_exit("killing child");
                        id = waitpid(child_id, &status, 0);
                        if (id < 0 || id != child_id)
                                error_exit("waiting for child");

                } else { /* Child */

                        close(fd);
                        printf("Test cycle on slave pty %s\n", pts_name);
                        fd = open(pts_name, O_RDWR);
                        if (fd < 0)
                                error_exit("opening pty slave");

                        while (1) {
                                char pattern[] = "test\n";
                                if (write(fd, pattern, strlen(pattern)) < 0)
                                        error_exit("slave writing");
                        }

                }
        }

        /* never gets here */
        return 0;
}
Reported-by: NSasha Levin <levinsasha928@gmail.com>
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>