kernel/linux.git/include/linux/tty.h, branch v4.0.7

pty: Fix input race when closing

2015-06-06T15:21:01+00:00

commit 1a48632ffed61352a7810ce089dc5a8bcd505a60 upstream. A read() from a pty master may mistakenly indicate EOF (errno == -EIO) after the pty slave has closed, even though input data remains to be read. For example, pty slave | input worker | pty master | | | | n_tty_read() pty_write() | | input avail? no add data | | sleep schedule worker --->| | . |---> flush_to_ldisc() | . pty_close() | fill read buffer | . wait for worker | wakeup reader --->| . | read buffer full? |---> input avail ? yes |<--- yes - exit worker | copy 4096 bytes to user TTY_OTHER_CLOSED <---| |<--- kick worker | | **** New read() before worker starts **** | | n_tty_read() | | input avail? no | | TTY_OTHER_CLOSED? yes | | return -EIO Several conditions are required to trigger this race: 1. the ldisc read buffer must become full so the input worker exits 2. the read() count parameter must be >= 4096 so the ldisc read buffer is empty 3. the subsequent read() occurs before the kicked worker has processed more input However, the underlying cause of the race is that data is pipelined, while tty state is not; ie., data already written by the pty slave end is not yet visible to the pty master end, but state changes by the pty slave end are visible to the pty master end immediately. Pipeline the TTY_OTHER_CLOSED state through input worker to the reader. 1. Introduce TTY_OTHER_DONE which is set by the input worker when TTY_OTHER_CLOSED is set and either the input buffers are flushed or input processing has completed. Readers/polls are woken when TTY_OTHER_DONE is set. 2. Reader/poll checks TTY_OTHER_DONE instead of TTY_OTHER_CLOSED. 3. A new input worker is started from pty_close() after setting TTY_OTHER_CLOSED, which ensures the TTY_OTHER_DONE state will be set if the last input worker is already finished (or just about to exit). Remove tty_flush_to_ldisc(); no in-tree callers. Fixes: 52bce7f8d4fc ("pty, n_tty: Simplify input processing on final close") Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=96311 BugLink: http://bugs.launchpad.net/bugs/1429756 Reported-by: Andy Whitcroft Reported-by: H.J. Lu Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman

tty: Remove external interface for tty_set_termios()

2015-02-02T18:11:28+00:00

tty_set_termios() is an internal helper intended for file scope use. UART drivers which are capable of driving the RTS pin must properly handle the tiocmset() method, regardless of termios settings. A failure to do so is a UART driver bug and should be fixed there. Do not use this interface to workaround UART driver bugs. Cc: Johan Hedberg Cc: Signed-off-by: Peter Hurley Acked-by: Marcel Holtmann Signed-off-by: Greg Kroah-Hartman

n_tty: Fix signal handling flushes

2015-02-02T18:11:27+00:00

BRKINT and ISIG requires input and output flush when a signal char is received. However, the order of operations is significant since parallel i/o may be ongoing. Merge the signal handling for BRKINT with ISIG handling. Process the signal first. This ensures any ongoing i/o is aborted; without this, a waiting writer may continue writing after the flush occurs and after the signal char has been echoed. Write lock the termios_rwsem, which excludes parallel writers from pushing new i/o until after the output buffers are flushed; claiming the write lock is necessary anyway to exclude parallel readers while the read buffer is flushed. Subclass the termios_rwsem for ptys since the slave pty performing the flush may appear to reorder the termios_rwsem->tty buffer lock lock order; adding annotation clarifies that slave tty_buffer lock-> slave termios_rwsem -> master tty_buffer lock is a valid lock order. Flush the echo buffer. In this context, the echo buffer is 'output'. Otherwise, the output will appear discontinuous because the output buffer was cleared which contains older output than the echo buffer. Open-code the read buffer flush since the input worker does not need kicking (this is the input worker). Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman

pty: Fix buffer flush deadlock

2015-02-02T18:11:27+00:00

The pty driver does not clear its write buffer when commanded. This is to avoid an apparent deadlock between parallel flushes from both pty ends; specifically when handling either BRK or INTR input. However, parallel flushes from this source is not possible since the pty master can never be set to BRKINT or ISIG. Parallel flushes from other sources are possible but these do not threaten deadlocks. Annotate the tty buffer mutex for lockdep to represent the nested tty_buffer locking which occurs when the pty slave is processing input (its buffer mutex held) and receives INTR or BRK and acquires the linked tty buffer mutex via tty_buffer_flush(). Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman

tty: Make lock subclasses available for other tty locks

2015-02-02T18:11:27+00:00

Besides nested legacy_mutex locking which is required on pty pair teardown, other nested pty operations require lock subclassing. Move lock subclass definition to tty interface header, include/linux/tty.h, and document its use. Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman

tty: Convert tty->closing to int

2014-11-06T22:57:27+00:00

tty->closing is a bitfield member; prevent corruption from non-atomic update by assigning a unique memory location. Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman

tty: Remove defunct serial_console_init() declaration

2014-11-06T04:18:30+00:00

serial_console_init() is not defined by the tty core; remove declaration. Note that the powerpc arch boot code contains a serial_console_init() declaration in arch/powerpc/boot/ops.h which is restricted to the powerpc arch boot. Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman

tty: Remove defunct pcxe_open() declaration

2014-11-06T04:18:30+00:00

pcxe_open() has no definition in mainline; remove declaration. Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman

tty: Flush ldisc buffer atomically with tty flip buffers

2014-11-06T02:50:43+00:00

tty_ldisc_flush() first clears the line discipline input buffer, then clears the tty flip buffers. However, this allows for existing data in the tty flip buffers to be added after the ldisc input buffer has been cleared, but before the flip buffers have been cleared. Add an optional ldisc parameter to tty_buffer_flush() to allow tty_ldisc_flush() to pass the ldisc to clear. NB: Initially, the plan was to do this automatically in tty_buffer_flush(). However, an audit of the behavior of existing line disciplines showed that performing a ldisc buffer flush on ioctl(TCFLSH) was not always the outcome. For example, some line disciplines have flush_buffer() methods but not ioctl() methods, so a ->flush_buffer() command would be unexpected. Reviewed-by: Alan Cox Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman

tty: Remove tty_unhangup() declaration

2014-11-06T02:50:42+00:00

The tty_unhangup() function is not defined. Reviewed-by: Alan Cox Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman