n_tty: Fix signal handling flushes
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 <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -1090,16 +1090,45 @@ static void eraser(unsigned char c, struct tty_struct *tty)
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* Called when a signal is being sent due to terminal input.
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* Called when a signal is being sent due to terminal input.
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* Called from the driver receive_buf path so serialized.
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* Called from the driver receive_buf path so serialized.
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*
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*
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* Performs input and output flush if !NOFLSH. In this context, the echo
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* buffer is 'output'. The signal is processed first to alert any current
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* readers or writers to discontinue and exit their i/o loops.
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*
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* Locking: ctrl_lock
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* Locking: ctrl_lock
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*/
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*/
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static void isig(int sig, struct tty_struct *tty)
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static void isig(int sig, struct tty_struct *tty)
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{
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{
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struct n_tty_data *ldata = tty->disc_data;
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struct pid *tty_pgrp = tty_get_pgrp(tty);
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struct pid *tty_pgrp = tty_get_pgrp(tty);
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if (tty_pgrp) {
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if (tty_pgrp) {
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kill_pgrp(tty_pgrp, sig, 1);
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kill_pgrp(tty_pgrp, sig, 1);
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put_pid(tty_pgrp);
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put_pid(tty_pgrp);
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}
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}
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if (!L_NOFLSH(tty)) {
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up_read(&tty->termios_rwsem);
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down_write(&tty->termios_rwsem);
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/* clear echo buffer */
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mutex_lock(&ldata->output_lock);
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ldata->echo_head = ldata->echo_tail = 0;
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ldata->echo_mark = ldata->echo_commit = 0;
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mutex_unlock(&ldata->output_lock);
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/* clear output buffer */
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tty_driver_flush_buffer(tty);
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/* clear input buffer */
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reset_buffer_flags(tty->disc_data);
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/* notify pty master of flush */
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if (tty->link)
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n_tty_packet_mode_flush(tty);
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up_write(&tty->termios_rwsem);
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down_read(&tty->termios_rwsem);
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}
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}
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}
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/**
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/**
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@ -1123,13 +1152,6 @@ static void n_tty_receive_break(struct tty_struct *tty)
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return;
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return;
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if (I_BRKINT(tty)) {
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if (I_BRKINT(tty)) {
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isig(SIGINT, tty);
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isig(SIGINT, tty);
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if (!L_NOFLSH(tty)) {
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/* flushing needs exclusive termios_rwsem */
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up_read(&tty->termios_rwsem);
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n_tty_flush_buffer(tty);
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tty_driver_flush_buffer(tty);
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down_read(&tty->termios_rwsem);
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}
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return;
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return;
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}
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}
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if (I_PARMRK(tty)) {
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if (I_PARMRK(tty)) {
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@ -1203,13 +1225,7 @@ static void n_tty_receive_parity_error(struct tty_struct *tty, unsigned char c)
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static void
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static void
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n_tty_receive_signal_char(struct tty_struct *tty, int signal, unsigned char c)
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n_tty_receive_signal_char(struct tty_struct *tty, int signal, unsigned char c)
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{
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{
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if (!L_NOFLSH(tty)) {
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isig(signal, tty);
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/* flushing needs exclusive termios_rwsem */
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up_read(&tty->termios_rwsem);
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n_tty_flush_buffer(tty);
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tty_driver_flush_buffer(tty);
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down_read(&tty->termios_rwsem);
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}
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if (I_IXON(tty))
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if (I_IXON(tty))
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start_tty(tty);
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start_tty(tty);
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if (L_ECHO(tty)) {
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if (L_ECHO(tty)) {
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@ -1217,7 +1233,6 @@ n_tty_receive_signal_char(struct tty_struct *tty, int signal, unsigned char c)
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commit_echoes(tty);
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commit_echoes(tty);
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} else
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} else
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process_echoes(tty);
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process_echoes(tty);
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isig(signal, tty);
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return;
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return;
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}
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}
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@ -395,6 +395,7 @@ static int pty_common_install(struct tty_driver *driver, struct tty_struct *tty,
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goto err_put_module;
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goto err_put_module;
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tty_set_lock_subclass(o_tty);
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tty_set_lock_subclass(o_tty);
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lockdep_set_subclass(&o_tty->termios_rwsem, TTY_LOCK_SLAVE);
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if (legacy) {
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if (legacy) {
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/* We always use new tty termios data so we can do this
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/* We always use new tty termios data so we can do this
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@ -25,6 +25,9 @@
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*
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*
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* legacy_mutex - Nested tty locks are necessary for releasing pty pairs.
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* legacy_mutex - Nested tty locks are necessary for releasing pty pairs.
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* The stable lock order is master pty first, then slave pty.
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* The stable lock order is master pty first, then slave pty.
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* termios_rwsem - The stable lock order is tty_buffer lock->termios_rwsem.
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* Subclassing this lock enables the slave pty to hold its
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* termios_rwsem when claiming the master tty_buffer lock.
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* tty_buffer lock - slave ptys can claim nested buffer lock when handling
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* tty_buffer lock - slave ptys can claim nested buffer lock when handling
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* signal chars. The stable lock order is slave pty, then
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* signal chars. The stable lock order is slave pty, then
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* master.
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* master.
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