tty: Fix high cpu load if tty is unreleaseable

Kernel oops can cause the tty to be unreleaseable (for example, if
n_tty_read() crashes while on the read_wait queue). This will cause
tty_release() to endlessly loop without sleeping.

Use a killable sleep timeout which grows by 2n+1 jiffies over the interval
[0, 120 secs.) and then jumps to forever (but still killable).

NB: killable just allows for the task to be rewoken manually, not
to be terminated.

Cc: <stable@vger.kernel.org> # since before 2.6.32
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 16a2c02..4021c10 100644 (file)
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1709,6 +1709,7 @@ int tty_release(struct inode *inode, struct file *filp)
        int     pty_master, tty_closing, o_tty_closing, do_sleep;
        int     idx;
        char    buf[64];
+       long    timeout = 0;
 
        if (tty_paranoia_check(tty, inode, __func__))
                return 0;
@@ -1793,7 +1794,11 @@ int tty_release(struct inode *inode, struct file *filp)
                                __func__, tty_name(tty, buf));
                tty_unlock_pair(tty, o_tty);
                mutex_unlock(&tty_mutex);
-               schedule();
+               schedule_timeout_killable(timeout);
+               if (timeout < 120 * HZ)
+                       timeout = 2 * timeout + 1;
+               else
+                       timeout = MAX_SCHEDULE_TIMEOUT;
        }
 
        /*