On Wed, Feb 14, 2018 at 06:57:06AM +1100, NeilBrown wrote:
> I think this change is safe. It is a bit of a hack, but the "flush"
> interface was actually very poorly designed and I don't think it *can*
> be implemented cleanly.
> Maybe we should just ignore the number written in and *always* flush
> the cache completely. That is was it always wanted.
>
> See below.
>
> Bruce: do you have any thoughts on this?
I'm fine with ignoring the number--I agree that the chance anyone is
doing anything fancier is vanishingly small.
--b.
>
> Thanks,
> NeilBrown
>
> diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
> index aa36dad32db1..43f117d1547e 100644
> --- a/net/sunrpc/cache.c
> +++ b/net/sunrpc/cache.c
> @@ -1450,7 +1450,7 @@ static ssize_t write_flush(struct file *file, const char __user *buf,
> struct cache_detail *cd)
> {
> char tbuf[20];
> - char *bp, *ep;
> + char *ep;
> time_t then, now;
>
> if (*ppos || count > sizeof(tbuf)-1)
> @@ -1461,24 +1461,24 @@ static ssize_t write_flush(struct file *file, const char __user *buf,
> simple_strtoul(tbuf, &ep, 0);
> if (*ep && *ep != '\n')
> return -EINVAL;
> + /* Note that while we check that 'buf' holds a valid number,
> + * we always ignore the value and just flush everything.
> + * Making use of the number leads to races.
> + */
>
> - bp = tbuf;
> - then = get_expiry(&bp);
> now = seconds_since_boot();
> - cd->nextcheck = now;
> - /* Can only set flush_time to 1 second beyond "now", or
> + /* Always flush everything, so behave like cache_purge()
> + * Can only set flush_time to 1 second beyond "now", or
> * possibly 1 second beyond flushtime. This is because
> * flush_time never goes backwards so it mustn't get too far
> * ahead of time.
> */
> - if (then >= now) {
> - /* Want to flush everything, so behave like cache_purge() */
> - if (cd->flush_time >= now)
> - now = cd->flush_time + 1;
> - then = now;
> - }
>
> - cd->flush_time = then;
> + if (cd->flush_time >= now)
> + now = cd->flush_time + 1;
> +
> + cd->flush_time = now;
> + cd->nextcheck = now;
> cache_flush();
>
> *ppos += count;
>
>
> >
> > --------------------------------------------------------------------------
> > then = get_expiry(&bp);
> > now = seconds_since_boot();
> > cd->nextcheck = now;
> > /* Can only set flush_time to 1 second beyond "now", or
> > * possibly 1 second beyond flushtime. This is because
> > * flush_time never goes backwards so it mustn't get too far
> > * ahead of time.
> > */
> > if (then != now)
> > printk("%s %d then = %d, now = %d\n", __func__, __LINE__, then, now);
> > - if (then >= now) {
> > + if (then >= now - 1) {
> > /* Want to flush eve
--
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