linux-toradex.git/drivers/tty/n_tty.c, branch v3.0.93

TTY: Fix tty miss restart after we turn off flow-control

2013-06-07T19:46:35+00:00

commit dab73b4eb9ef924a2b90dab84e539076d82b256f upstream.

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=465823

Signed-off-by: Wang YanQing 
Signed-off-by: Greg Kroah-Hartman

Remove BUG_ON from n_tty_read()

2012-10-07T15:27:24+00:00

commit e9490e93c1978b6669f3e993caa3189be13ce459 upstream.

Change the BUG_ON to WARN_ON and return in case of tty->read_buf==NULL. We want to track a
couple of long standing reports of this but at the same time we can avoid killing the box.

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

TTY: ntty, add one more sanity check

2011-06-07T17:36:47+00:00

With the previous patch, we fixed another bug where read_buf was freed
while we still was in n_tty_read. We currently check whether read_buf
is NULL at the start of the function. Add one more check after we wake
up from waiting for input.

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

Revert "tty: make receive_buf() return the amout of bytes received"

2011-06-03T21:33:24+00:00

This reverts commit b1c43f82c5aa265442f82dba31ce985ebb7aa71c.

It was broken in so many ways, and results in random odd pty issues.

It re-introduced the buggy schedule_work() in flush_to_ldisc() that can
cause endless work-loops (see commit a5660b41af6a: "tty: fix endless
work loop when the buffer fills up").

It also used an "unsigned int" return value fo the ->receive_buf()
function, but then made multiple functions return a negative error code,
and didn't actually check for the error in the caller.

And it didn't actually work at all.  BenH bisected down odd tty behavior
to it:
  "It looks like the patch is causing some major malfunctions of the X
   server for me, possibly related to PTYs.  For example, cat'ing a
   large file in a gnome terminal hangs the kernel for -minutes- in a
   loop of what looks like flush_to_ldisc/workqueue code, (some ftrace
   data in the quoted bits further down).

   ...

   Some more data: It -looks- like what happens is that the
   flush_to_ldisc work queue entry constantly re-queues itself (because
   the PTY is full ?) and the workqueue thread will basically loop
   forver calling it without ever scheduling, thus starving the consumer
   process that could have emptied the PTY."

which is pretty much exactly the problem we fixed in a5660b41af6a.

Milton Miller pointed out the 'unsigned int' issue.

Reported-by: Benjamin Herrenschmidt 
Reported-by: Milton Miller 
Cc: Stefan Bigler 
Cc: Toby Gray 
Cc: Felipe Balbi 
Cc: Greg Kroah-Hartman 
Cc: Alan Cox 
Signed-off-by: Linus Torvalds

tty: make receive_buf() return the amout of bytes received

2011-04-23T00:31:53+00:00

it makes it simpler to keep track of the amount of
bytes received and simplifies how flush_to_ldisc counts
the remaining bytes. It also fixes a bug of lost bytes
on n_tty when flushing too many bytes via the USB
serial gadget driver.

Tested-by: Stefan Bigler 
Tested-by: Toby Gray 
Signed-off-by: Felipe Balbi 
Signed-off-by: Greg Kroah-Hartman

tty: fix endless work loop when the buffer fills up

2011-04-04T21:26:54+00:00

Commit f23eb2b2b285 ('tty: stop using "delayed_work" in the tty layer')
ended up causing hung machines on UP with no preemption, because the
work routine to flip the buffer data to the ldisc would endlessly re-arm
itself if the destination buffer had filled up.

With the delayed work, that only caused a timer-driving polling of the
tty state every timer tick, but without the delay we just ended up with
basically a busy loop instead.

Stop the insane polling, and instead make the code that opens up the
receive room re-schedule the buffer flip work.  That's what we should
have been doing anyway.

This same "poll for tty room" issue is almost certainly also the cause
of excessive kworker activity when idle reported by Dave Jones, who also
reported "flush_to_ldisc executing 2500 times a second" back in Nov 2010:

  http://lkml.org/lkml/2010/11/30/592

which is that silly flushing done every timer tick.  Wasting both power
and CPU for no good reason.

Reported-and-tested-by: Alexander Beregalov 
Reported-and-tested-by: Sitsofe Wheeler 
Cc: Greg KH 
Cc: Alan Cox 
Cc: Dave Jones 
Signed-off-by: Linus Torvalds

TTY: create drivers/tty and move the tty core files there

2010-11-05T15:10:33+00:00

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 

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