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tty: fix up atime/mtime mess, take three

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We first tried to avoid updating atime/mtime entirely (commit
b0de59b573: "TTY: do not update atime/mtime on read/write"), and then
limited it to only update it occasionally (commit 37b7f3c765: "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 <sim@hostway.ca>
Acked-by: Jiri Slaby <jslaby@suse.cz>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2013-05-01 07:32:21 -07:00
commit b0b885657b
2 changed files with 5 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

3
drivers/tty/pty.c
View file

@ -681,6 +681,9 @@ static int ptmx_open(struct inode *inode, struct file *filp)
nonseekable_open(inode, 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); retval = tty_alloc_file(filp);
if (retval) if (retval)
return retval; return retval;

4
drivers/tty/tty_io.c
View file

@ -988,10 +988,10 @@ void start_tty(struct tty_struct *tty)
EXPORT_SYMBOL(start_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) static void tty_update_time(struct timespec *time)
{ {
unsigned long sec = get_seconds(); unsigned long sec = get_seconds() & ~7;
sec -= sec % 60;
if ((long)(sec - time->tv_sec) > 0) if ((long)(sec - time->tv_sec) > 0)
time->tv_sec = sec; time->tv_sec = sec;
} }