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tty: Fix high cpu load if tty is unreleaseable

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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>
This commit is contained in:
Peter Hurley 2014-10-16 13:51:30 -04:00 committed by Greg Kroah-Hartman
parent 547039ec50
commit 37b1645788
1 changed files with 6 additions and 1 deletions
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7
drivers/tty/tty_io.c
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@ -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;
}
/*