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[PATCH v2 02/10] tty: Retry failed reopen if tty teardown in-progress

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A small window exists where a tty reopen will observe the tty
just prior to imminent teardown (tty->count == 0); in this case, open()
returns EIO to userspace.

Instead, retry the open after checking for signals and yielding;
this interruptible retry loop allows teardown to commence and initialize
a new tty on retry. Never retry the BSD master pty reopen; there is no
guarantee the pty pair teardown is imminent since the slave file
descriptors may remain open indefinitely.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
---
 drivers/tty/tty_io.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 1bf67a2..93fe10d 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1468,13 +1468,13 @@ static int tty_reopen(struct tty_struct *tty)
 {
 	struct tty_driver *driver = tty->driver;
 
-	if (!tty->count)
-		return -EIO;
-
 	if (driver->type == TTY_DRIVER_TYPE_PTY &&
 	    driver->subtype == PTY_TYPE_MASTER)
 		return -EIO;
 
+	if (!tty->count)
+		return -EAGAIN;
+
 	if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN))
 		return -EBUSY;
 
@@ -2094,7 +2094,11 @@ retry_open:
 
 	if (IS_ERR(tty)) {
 		retval = PTR_ERR(tty);
-		goto err_file;
+		if (retval != -EAGAIN || signal_pending(current))
+			goto err_file;
+		tty_free_file(filp);
+		schedule();
+		goto retry_open;
 	}
 
 	tty_add_file(tty, filp);
-- 
2.7.0

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[PATCH v2 00/10] Rework tty_reopen() Peter Hurley <peter@hurleysoftware.com> - 2016-01-10 06:20 +0100
  [PATCH v2 01/10] tty: Wait interruptibly for tty lock on reopen Peter Hurley <peter@hurleysoftware.com> - 2016-01-10 06:20 +0100
  [PATCH v2 06/10] tty: Re-declare tty_driver_remove_tty() file scope Peter Hurley <peter@hurleysoftware.com> - 2016-01-10 06:20 +0100
  [PATCH v2 03/10] tty: Fix ldisc leak in failed tty_init_dev() Peter Hurley <peter@hurleysoftware.com> - 2016-01-10 06:20 +0100
  [PATCH v2 05/10] tty: Fix tty_init_termios() declaration Peter Hurley <peter@hurleysoftware.com> - 2016-01-10 06:20 +0100
  [PATCH v2 04/10] tty: Remove !tty check from free_tty_struct() Peter Hurley <peter@hurleysoftware.com> - 2016-01-10 06:20 +0100
  [PATCH v2 07/10] pty: Remove pty_unix98_shutdown() Peter Hurley <peter@hurleysoftware.com> - 2016-01-10 06:20 +0100
  [PATCH v2 08/10] tty: Remove __lockfunc annotation from tty lock functions Peter Hurley <peter@hurleysoftware.com> - 2016-01-10 06:20 +0100
  [PATCH v2 02/10] tty: Retry failed reopen if tty teardown in-progress Peter Hurley <peter@hurleysoftware.com> - 2016-01-10 06:20 +0100
  [PATCH v2 09/10] tty: Consolidate noctty checks in tty_open() Peter Hurley <peter@hurleysoftware.com> - 2016-01-10 06:20 +0100
  [PATCH v2 10/10] tty: Refactor tty_open() Peter Hurley <peter@hurleysoftware.com> - 2016-01-10 06:20 +0100

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