Refactor the implementation of n_tty_write() into do_n_tty_write(),
and change n_tty_write() to call do_n_tty_write() after acquiring
tty.termios_rwsem.
This allows the n_tty line dicipline to write to a user tty via
do_n_tty_write() when already holding tty.termios_rwsem.
Signed-off-by: Walt Drummond <w...@drummond.us>
---
drivers/tty/n_tty.c | 69 +++++++++++++++++++++++++++------------------
include/linux/tty.h | 2 +-
2 files changed, 42 insertions(+), 29 deletions(-)
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 0ec93f1a61f5..64a058a4c63b 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -2231,45 +2231,24 @@ static ssize_t n_tty_read(struct tty_struct *tty,
struct file *file,
return retval;
}
-/**
- * n_tty_write - write function for tty
- * @tty: tty device
- * @file: file object
- * @buf: userspace buffer pointer
- * @nr: size of I/O
- *
- * Write function of the terminal device. This is serialized with
- * respect to other write callers but not to termios changes, reads
- * and other such events. Since the receive code will echo characters,
- * thus calling driver write methods, the output_lock is used in
- * the output processing functions called here as well as in the
- * echo processing function to protect the column state and space
- * left in the buffer.
- *
- * This code must be sure never to sleep through a hangup.
- *
- * Locking: output_lock to protect column state and space left
- * (note that the process_output*() functions take this
- * lock themselves)
- */
-
-static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
- const unsigned char *buf, size_t nr)
+static ssize_t do_n_tty_write(struct tty_struct *tty, struct file *file,
+ const unsigned char *buf, size_t nr)
{
const unsigned char *b = buf;
DEFINE_WAIT_FUNC(wait, woken_wake_function);
int c;
ssize_t retval = 0;
+ lockdep_assert_held_read(&tty->termios_rwsem);
+
/* Job control check -- must be done at start (POSIX.1 7.1.1.4). */
- if (L_TOSTOP(tty) && file->f_op->write_iter != redirected_tty_write) {
+ if (L_TOSTOP(tty) &&
+ !(file && file->f_op->write_iter != redirected_tty_write)) {
retval = tty_check_change(tty);
if (retval)
return retval;
}
- down_read(&tty->termios_rwsem);
-
/* Write out any echoed characters that are still pending */
process_echoes(tty);
@@ -2336,10 +2315,44 @@ static ssize_t n_tty_write(struct tty_struct *tty,
struct file *file,
remove_wait_queue(&tty->write_wait, &wait);
if (nr && tty->fasync)
set_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
- up_read(&tty->termios_rwsem);
+
return (b - buf) ? b - buf : retval;
}
+/**
+ * n_tty_write - write function for tty
+ * @tty: tty device
+ * @file: file object
+ * @buf: userspace buffer pointer
+ * @nr: size of I/O
+ *
+ * Write function of the terminal device. This is serialized with
+ * respect to other write callers but not to termios changes, reads
+ * and other such events. Since the receive code will echo characters,
+ * thus calling driver write methods, the output_lock is used in
+ * the output processing functions called here as well as in the
+ * echo processing function to protect the column state and space
+ * left in the buffer.
+ *
+ * This code must be sure never to sleep through a hangup.
+ *
+ * Locking: output_lock to protect column state and space left
+ * (note that the process_output*() functions take this
+ * lock themselves)
+ */
+
+static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
+ const unsigned char *buf, size_t nr)
+{
+ ssize_t retval = 0;
+
+ down_read(&tty->termios_rwsem);
+ retval = do_n_tty_write(tty, file, buf, nr);
+ up_read(&tty->termios_rwsem);
+
+ return retval;
+}
+
/**
* n_tty_poll - poll method for N_TTY
* @tty: terminal device
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 168e57e40bbb..cbe5d535a69d 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -237,7 +237,7 @@ struct tty_file_private {
static inline bool tty_io_nonblock(struct tty_struct *tty, struct file *file)
{
- return file->f_flags & O_NONBLOCK ||
+ return (file && file->f_flags & O_NONBLOCK) ||
test_bit(TTY_LDISC_CHANGING, &tty->flags);
}
--
2.30.2
