From: Linus Torvalds Date: Wed, 1 May 2013 14:32:21 +0000 (-0700) Subject: tty: fix up atime/mtime mess, take three X-Git-Tag: v3.4.44~45 X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=ce5b62fd947369813666074f725aa0c1d819fc29;p=karo-tx-linux.git tty: fix up atime/mtime mess, take three commit b0b885657b6c8ef63a46bc9299b2a7715d19acde upstream. We first tried to avoid updating atime/mtime entirely (commit b0de59b5733d: "TTY: do not update atime/mtime on read/write"), and then limited it to only update it occasionally (commit 37b7f3c76595: "TTY: fix atime/mtime regression"), but it turns out that this was both insufficient and overkill. It was insufficient because we let people attach to the shared ptmx node to see activity without even reading atime/mtime, and it was overkill because the "only once a minute" means that you can't really tell an idle person from an active one with 'w'. So this tries to fix the problem properly. It marks the shared ptmx node as un-notifiable, and it lowers the "only once a minute" to a few seconds instead - still long enough that you can't time individual keystrokes, but short enough that you can tell whether somebody is active or not. Reported-by: Simon Kirby Acked-by: Jiri Slaby Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c index 636c539cb77a..cf9a1911d4ab 100644 --- a/drivers/tty/pty.c +++ b/drivers/tty/pty.c @@ -607,6 +607,9 @@ static int ptmx_open(struct inode *inode, struct file *filp) nonseekable_open(inode, filp); + /* We refuse fsnotify events on ptmx, since it's a shared resource */ + filp->f_mode |= FMODE_NONOTIFY; + retval = tty_alloc_file(filp); if (retval) return retval; diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index bf9f98750f4f..b28d6356a142 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -938,10 +938,10 @@ void start_tty(struct tty_struct *tty) EXPORT_SYMBOL(start_tty); +/* We limit tty time update visibility to every 8 seconds or so. */ static void tty_update_time(struct timespec *time) { - unsigned long sec = get_seconds(); - sec -= sec % 60; + unsigned long sec = get_seconds() & ~7; if ((long)(sec - time->tv_sec) > 0) time->tv_sec = sec; }