Messages in this thread | | | Date | Fri, 19 Aug 2005 16:12:23 -0700 | From | "Paul E. McKenney" <> | Subject | Re: 2.6.13-rc6-rt6 |
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On Fri, Aug 19, 2005 at 07:02:42PM -0400, Steven Rostedt wrote: > On Fri, 2005-08-19 at 15:47 -0700, Paul E. McKenney wrote: > > > Good catch -- but a few changes needed to be perfectly safe: > > > > static inline void *netpoll_poll_lock(struct net_device *dev) > > { > > > > struct netpoll_info *npi; > > > > rcu_read_lock(); > > npi = rcu_dereference(dev)->npinfo; > > if (have) { > > Here I'm sure you mean "if (npi) {" :-)
Right you are! ;-)
> > spin_lock(&npi->poll_lock); > > npi->poll_owner = smp_processor_id(); > > return npi; > > } > > return NULL; > > } > > > > The earlier version could get in trouble if dev->npinfo was set > > to NULL while this was executing. > > Truth be told, I was just fixing the race with getting the npinfo > pointer set between netpoll_poll_lock and netpoll_poll_unlock. I wrote > a patch that fixed that but nothing with the rcu_locks. Then I looked > at the current git tree and saw that they already had my changes, but > also included the rcu locks. So I just (blindly) added them.
Understood!
> > Again, I do not fully understand this code, so a grain of salt might > > come in handy. But there definitely need to be some rcu_dereference() > > and rcu_assign_pointer() primitives in there somewhere. ;-) > > > > The following changes look good to me, but, as I said earlier, I do > > not claim to fully understand this code. > > netpoll has changed quite a bit in the last few releases. I've seen lots > of fixup code sent in (which usually means there's lots of new broken > code ;-) > > Anyway, I don't quite fully understand RCU. I read a few of the > documents on your web site, but I haven't had time to really digest it. > Have you taken a look at the latest git tree? The rcu_locks are used > for net poll quite a bit more there.
Hmmm.... Guess it is time for me to stop procrastinating on better understanding git...
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