Hi Bruce! On Thu, 2008-08-14 at 15:06 -0400, J. Bruce Fields wrote: > On Thu, Aug 14, 2008 at 08:08:16PM +0900, NAKANO Hiroaki wrote: > > lockd uses time_before() to determine whether the grace period has > > expired. This would seem to be enough to avoid timer wrap-around issues, > > but, unfortunately, that is not the case. The time_* family of > > comparison functions can be safely used to compare jiffies relatively > > close in time, but they stop working after approximately LONG_MAX/2 > > ticks. nfsd can suffer this problem because the time_before() comparison > > in lockd() is not performed until the first request comes in, which > > means that if there is no lockd traffic for more than LONG_MAX/2 ticks > > we are screwed. > > > > The implication of this is that once time_before() starts misbehaving > > any attempt from a NFS client to execute fcntl() will be received with a > > NLM_LCK_DENIED_GRACE_PERIOD message for 25 days (assuming HZ=1000). In > > other words, the 50 seconds grace period could turn into a grace period > > of 50 days or more. > > > > This patch corrects this behavior by implementing grace period with a > > (retriggerable) timer. > > > > Note: This bug was analyzed independently by Oda-san <oda@xxxxxxxxxxxxx> > > and myself. > > Good catch! Did you actually run across this in practice? I would've > thought it relatively unusual to have a lockd that didn't receive its > first lock request until 25 days after startup. Yes, we did find this problem in production. More often than one would wish, installing new software in a system that has been running without a hiccup for weeks or months is the only thing you will need to bring mayhem. > I still have a mild preference for a work struct just in case we end up > wanting to do something slightly more complicated to end the grace > period, but I don't really have anything in mind. For simplicity I think we could we get Nakano-san's patch merged first. If needed, moving to a work-based solution should be relatively easily. Thank you for you comments! - Fernando -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
