To avoid a lock inversion deadlock, the pty driver must distinguish
when the flush_buffer() caller already holds its own tty_buffer buf->lock
(currently only in N_TTY's receive_buf() path when handling signals).
Extend tty_driver ops interface with the flush_nested() method.
Add the tty_driver_flush_nested() accessor which uses flush_nested()
(if the driver declares it); otherwise, uses tty_driver_flush_buffer().
Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
---
drivers/tty/n_tty.c | 4 ++--
drivers/tty/tty_ioctl.c | 21 +++++++++++++++++++++
include/linux/tty.h | 1 +
include/linux/tty_driver.h | 1 +
4 files changed, 25 insertions(+), 2 deletions(-)
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index bd01d97..72a5c32 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -1191,7 +1191,7 @@ static void n_tty_receive_break(struct tty_struct *tty)
/* flushing needs exclusive termios_rwsem */
up_read(&tty->termios_rwsem);
n_tty_flush_buffer(tty);
- tty_driver_flush_buffer(tty);
+ tty_driver_flush_nested(tty);
down_read(&tty->termios_rwsem);
}
return;
@@ -1271,7 +1271,7 @@ n_tty_receive_signal_char(struct tty_struct *tty, int signal, unsigned char c)
/* flushing needs exclusive termios_rwsem */
up_read(&tty->termios_rwsem);
n_tty_flush_buffer(tty);
- tty_driver_flush_buffer(tty);
+ tty_driver_flush_nested(tty);
down_read(&tty->termios_rwsem);
}
if (I_IXON(tty))
diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c
index 6fd60fe..e64eb23 100644
--- a/drivers/tty/tty_ioctl.c
+++ b/drivers/tty/tty_ioctl.c
@@ -90,6 +90,27 @@ void tty_driver_flush_buffer(struct tty_struct *tty)
EXPORT_SYMBOL(tty_driver_flush_buffer);
/**
+ * tty_driver_flush_nested - discard internal buffer
+ * @tty: terminal
+ *
+ * Line disciplines must call this flavor of tty_driver_flush_buffer()
+ * if calling from their .receive_buf() method. The pty driver
+ * in particular requires special handling to avoid a lock inversion
+ * deadlock (see tty_buffer_flush_nested()).
+ *
+ * A normal flush_buffer() is performed for drivers without this
+ * extension.
+ */
+void tty_driver_flush_nested(struct tty_struct *tty)
+{
+ if (tty->ops->flush_nested)
+ tty->ops->flush_nested(tty);
+ else
+ tty_driver_flush_buffer(tty);
+}
+EXPORT_SYMBOL(tty_driver_flush_nested);
+
+/**
* tty_throttle - flow control
* @tty: terminal
*
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 9d234dc..de1f85f 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -414,6 +414,7 @@ extern int tty_put_char(struct tty_struct *tty, unsigned char c);
extern int tty_chars_in_buffer(struct tty_struct *tty);
extern int tty_write_room(struct tty_struct *tty);
extern void tty_driver_flush_buffer(struct tty_struct *tty);
+extern void tty_driver_flush_nested(struct tty_struct *tty);
extern void tty_throttle(struct tty_struct *tty);
extern void tty_unthrottle(struct tty_struct *tty);
extern int tty_throttle_safe(struct tty_struct *tty);
diff --git a/include/linux/tty_driver.h b/include/linux/tty_driver.h
index 756a609..4937e16 100644
--- a/include/linux/tty_driver.h
+++ b/include/linux/tty_driver.h
@@ -269,6 +269,7 @@ struct tty_operations {
void (*hangup)(struct tty_struct *tty);
int (*break_ctl)(struct tty_struct *tty, int state);
void (*flush_buffer)(struct tty_struct *tty);
+ void (*flush_nested)(struct tty_struct *tty);
void (*set_ldisc)(struct tty_struct *tty);
void (*wait_until_sent)(struct tty_struct *tty, int timeout);
void (*send_xchar)(struct tty_struct *tty, char ch);
--
1.8.1.2
--
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