Tom Tucker wrote: > Bruce: > > I'll take a look... > > Tom > > On Mon, 2008-02-18 at 12:45 -0500, J. Bruce Fields wrote: > >> On Sun, Feb 17, 2008 at 04:02:45PM -0500, Trond Myklebust wrote: >> >>> Hi Bruce, >>> >>> Here is a question for you. >>> >>> Why does svc_close_all() get away with deleting xprt->xpt_ready >>> without holding the pool->sp_lock? >>> >> >From a quick look--I think the intention is that the code that calls it >> (in svc_destroy()) is only called after all other server threads have >> exited, and that there can't be anyone else monkeying with that service >> any more. But I haven't verified that really carefully. >> That's certainly the intention. The serv->sv_nrthreads fields is used as a refcount, which counts 1 for each nfsd thread and sometimes 1 to guard some short-term manipulations. This refcount should not drop to zero until the last thread exits. So by the time svc_close_all() is called, no thread can be looking at a pool's sp_sockets list. Each xprt could still be racily added to that list from softirq mode data ready handlers calling svc_xprt_enqueue(), but only until the xprt's xpo_detach method is called (which removes any data ready callbacks). At that point, no code should be modifying the xpt_ready field, and it may or may not be used to link the xprt into some pool->sp_sockets but we don't care because all the pools are about to be destroyed anyway.
That's the way it's been working since 2.6.19, and I don't think any of Tom's patches changed that. I can think of a couple of things that could be wrong: * serv->sv_nrthreads is used in a few places, and there might be bugs in that which are getting that count wrong (when I left the code, all increments and decrements of that field went through svc_get() and svc_destroy(), but other changes have crept in). * Currently running data ready callbacks might be racing with xpo_detach. Moving that call inside the spin_lock_bh() critical section just after it might help. >>>> For more on this problem see >>>> http://marc.info/?l=linux-kernel&m=120293042005445 >>>> >>> There's the Bugzilla entry for it at >>> >>> > > > http://bugzilla.kernel.org/show_bug.cgi?id=9973 > It's not clear from the bugzilla that NFS is at fault here. -- Greg Banks, R&D Software Engineer, SGI Australian Software Group. The cake is *not* a lie. I don't speak for SGI. - To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
