linux-kernel - [PATCH 12/12] tty: Retry failed reopen if tty teardown in-progress

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Message-Id: <1448677557-16420-13-git-send-email-peter@hurleysoftware.com>
Date:	Fri, 27 Nov 2015 21:25:57 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Jiri Slaby <jslaby@...e.cz>, linux-kernel@...r.kernel.org,
	Peter Hurley <peter@...leysoftware.com>
Subject: [PATCH 12/12] tty: Retry failed reopen if tty teardown in-progress

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@...leysoftware.com>
---
 drivers/tty/tty_io.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index eb391d4..09e8d4f 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1465,13 +1465,13 @@ 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;
 
@@ -2095,8 +2095,13 @@ retry_open:
 		tty = tty_open_by_driver(device, inode, filp);
 
 	if (IS_ERR(tty)) {
+		tty_free_file(filp);
 		retval = PTR_ERR(tty);
-		goto err_file;
+		if (retval != -EAGAIN || signal_pending(current))
+			return retval;
+
+		schedule();
+		goto retry_open;
 	}
 
 	tty_add_file(tty, filp);
@@ -2165,9 +2170,6 @@ retry_open:
 	read_unlock(&tasklist_lock);
 	tty_unlock(tty);
 	return 0;
-err_file:
-	tty_free_file(filp);
-	return retval;
 }
 
 
-- 
2.6.3

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