From c96cf923a98d1b094df9f0cf97a83e118817e31b Mon Sep 17 00:00:00 2001 From: Dmitry Safonov Date: Thu, 1 Nov 2018 00:24:48 +0000 Subject: tty: Don't block on IO when ldisc change is pending There might be situations where tty_ldisc_lock() has blocked, but there is already IO on tty and it prevents line discipline changes. It might theoretically turn into dead-lock. Basically, provide more priority to pending tty_ldisc_lock() than to servicing reads/writes over tty. User-visible issue was reported by Mikulas where on pa-risc with Debian 5 reboot took either 80 seconds, 3 minutes or 3:25 after proper locking in tty_reopen(). Cc: Jiri Slaby Reported-by: Mikulas Patocka Signed-off-by: Dmitry Safonov Signed-off-by: Greg Kroah-Hartman --- drivers/tty/n_hdlc.c | 4 ++-- drivers/tty/n_r3964.c | 2 +- drivers/tty/n_tty.c | 8 ++++---- drivers/tty/tty_ldisc.c | 7 +++++++ 4 files changed, 14 insertions(+), 7 deletions(-) (limited to 'drivers/tty') diff --git a/drivers/tty/n_hdlc.c b/drivers/tty/n_hdlc.c index dabb391909aa..99460af61b77 100644 --- a/drivers/tty/n_hdlc.c +++ b/drivers/tty/n_hdlc.c @@ -612,7 +612,7 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file, } /* no data */ - if (file->f_flags & O_NONBLOCK) { + if (tty_io_nonblock(tty, file)) { ret = -EAGAIN; break; } @@ -679,7 +679,7 @@ static ssize_t n_hdlc_tty_write(struct tty_struct *tty, struct file *file, if (tbuf) break; - if (file->f_flags & O_NONBLOCK) { + if (tty_io_nonblock(tty, file)) { error = -EAGAIN; break; } diff --git a/drivers/tty/n_r3964.c b/drivers/tty/n_r3964.c index 749a608c40b0..f75696f0ee2d 100644 --- a/drivers/tty/n_r3964.c +++ b/drivers/tty/n_r3964.c @@ -1085,7 +1085,7 @@ static ssize_t r3964_read(struct tty_struct *tty, struct file *file, pMsg = remove_msg(pInfo, pClient); if (pMsg == NULL) { /* no messages available. */ - if (file->f_flags & O_NONBLOCK) { + if (tty_io_nonblock(tty, file)) { ret = -EAGAIN; goto unlock; } diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c index 3ad460219fd6..5dc9686697cf 100644 --- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c @@ -1702,7 +1702,7 @@ n_tty_receive_buf_common(struct tty_struct *tty, const unsigned char *cp, down_read(&tty->termios_rwsem); - while (1) { + do { /* * When PARMRK is set, each input char may take up to 3 chars * in the read buf; reduce the buffer space avail by 3x @@ -1744,7 +1744,7 @@ n_tty_receive_buf_common(struct tty_struct *tty, const unsigned char *cp, fp += n; count -= n; rcvd += n; - } + } while (!test_bit(TTY_LDISC_CHANGING, &tty->flags)); tty->receive_room = room; @@ -2211,7 +2211,7 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file, break; if (!timeout) break; - if (file->f_flags & O_NONBLOCK) { + if (tty_io_nonblock(tty, file)) { retval = -EAGAIN; break; } @@ -2365,7 +2365,7 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file, } if (!nr) break; - if (file->f_flags & O_NONBLOCK) { + if (tty_io_nonblock(tty, file)) { retval = -EAGAIN; break; } diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c index fc4c97cae01e..9434d20cf3ca 100644 --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -327,6 +327,11 @@ int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout) { int ret; + /* Kindly asking blocked readers to release the read side */ + set_bit(TTY_LDISC_CHANGING, &tty->flags); + wake_up_interruptible_all(&tty->read_wait); + wake_up_interruptible_all(&tty->write_wait); + ret = __tty_ldisc_lock(tty, timeout); if (!ret) return -EBUSY; @@ -337,6 +342,8 @@ int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout) void tty_ldisc_unlock(struct tty_struct *tty) { clear_bit(TTY_LDISC_HALTED, &tty->flags); + /* Can be cleared here - ldisc_unlock will wake up writers firstly */ + clear_bit(TTY_LDISC_CHANGING, &tty->flags); __tty_ldisc_unlock(tty); } -- cgit v1.2.3