Ilya Zykov 64325a3be0 tty: Correct tty buffer flush. ...

The root of problem is carelessly zeroing pointer(in function __tty_buffer_flush()),
when another thread can use it. It can be cause of "NULL pointer dereference".
  Main idea of the patch, this is never free last (struct tty_buffer) in the active buffer.
Only flush the data for ldisc(buf->head->read = buf->head->commit).
At that moment driver can collect(write) data in buffer without conflict.
It is repeat behavior of flush_to_ldisc(), only without feeding data to ldisc.

Also revert:
  commit c56a00a165
  tty: hold lock across tty buffer finding and buffer filling
In order to delete the unneeded locks any more.

Signed-off-by: Ilya Zykov <ilya@ilyx.ru>
CC: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2013-01-20 15:50:36 -08:00

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