Commit 37b16457 authored Oct 16, 2014 by Peter Hurley Committed by Greg Kroah-Hartman Nov 05, 2014

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>

parent 547039ec

drivers/tty/tty_io.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -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;
		}

		/*

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