Messages in this thread | | | Date | Sun, 25 Sep 2005 00:08:03 -0700 (PDT) | From | Vadim Lobanov <> | Subject | Re: [patch] sys_epoll_wait() timeout saga ... |
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On Sat, 24 Sep 2005, Andrew Morton wrote:
> Davide Libenzi <davidel@xmailserver.org> wrote: > > > > The attached patch uses the kernel min() macro, that is optimized has > > single compare by gcc-O2. Andrew, this goes over (hopefully ;) the bits > > you already have in -mm. > > OK, well I've rather lost the plot with all the patches flying around. > > I now have one single patch against epoll.c, below. Please confirm that > this is what was intended. If not, I'll drop it and let's start again. >
I hate to be the squeaky wheel here, but the attached patch is not 100% right -
> > From: Davide Libenzi <davidel@xmailserver.org> > > The sys_epoll_wait() function was not handling correctly negative timeouts > (besides -1), and like sys_poll(), was comparing millisec to secs in > testing the upper timeout limit. > > Signed-off-by: Davide Libenzi <davidel@xmailserver.org> > Signed-off-by: Andrew Morton <akpm@osdl.org> > --- > > fs/eventpoll.c | 8 ++++++-- > 1 files changed, 6 insertions(+), 2 deletions(-) > > diff -puN fs/eventpoll.c~sys_epoll_wait-fix-handling-of-negative-timeouts fs/eventpoll.c > --- devel/fs/eventpoll.c~sys_epoll_wait-fix-handling-of-negative-timeouts 2005-09-24 23:01:00.000000000 -0700 > +++ devel-akpm/fs/eventpoll.c 2005-09-24 23:02:50.000000000 -0700 > @@ -101,6 +101,10 @@ > /* Maximum number of poll wake up nests we are allowing */ > #define EP_MAX_POLLWAKE_NESTS 4 > > +/* Maximum msec timeout value storeable in a long int */ > +#define EP_MAX_MSTIMEO min(1000ULL * MAX_SCHEDULE_TIMEOUT / HZ, LONG_MAX / HZ - 1000ULL)
This should instead be: #define EP_MAX_MSTIMEO min(1000ULL * MAX_SCHEDULE_TIMEOUT / HZ, (LONG_MAX - 999ULL) / HZ) Here's why: We want to avoid overflow of (timeout * HZ + 999), or, in other words, the case where (timeout * HZ + 999) >= LONG_MAX Unwrapping the equation, we get timeout >= (LONG_MAX - 999) / HZ
The original code isn't _wrong_, but more restrictive than it should be. In any case, better to fix up the base patch now, before all the other patches go in. I could do this, or Davide can... it's all good. :-)
> + > + > struct epoll_filefd { > struct file *file; > int fd; > @@ -1506,8 +1510,8 @@ static int ep_poll(struct eventpoll *ep, > * and the overflow condition. The passed timeout is in milliseconds, > * that why (t * HZ) / 1000. > */ > - jtimeout = timeout == -1 || timeout > (MAX_SCHEDULE_TIMEOUT - 1000) / HZ ? > - MAX_SCHEDULE_TIMEOUT: (timeout * HZ + 999) / 1000; > + jtimeout = (timeout < 0 || timeout >= EP_MAX_MSTIMEO) ? > + MAX_SCHEDULE_TIMEOUT : (timeout * HZ + 999) / 1000; > > retry: > write_lock_irqsave(&ep->lock, flags); > _ > > -
-Vadim Lobanov - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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