On Fri, Nov 15, 2013 at 11:55:20AM -0600, Eric Sandeen wrote: > On 11/15/13, 11:19 AM, Eric Sandeen wrote: > > On 11/13/13, 7:16 PM, Dave Chinner wrote: > > > >> That's client side, not server side, so that's the NFS client inode > >> it is locking, not the server side XFS inode. > > > > Ah, geez, you're right. (x3) > > > > <snip> > > > >> Server side, where i_version is pulled out of an XFS inode: > >> > >> $ git grep i_version fs/nfsd > >> fs/nfsd/nfs3xdr.c: fhp->fh_post_change = fhp->fh_dentry->d_inode->i_version; > >> fs/nfsd/nfs4xdr.c: write64(p, inode->i_version); > >> fs/nfsd/nfsfh.h: fhp->fh_pre_change = inode->i_version; > >> $ > >> > >> the nfsfh.h hit is in fill_pre_wcc(), which appears to be called > >> under i_mutex but not i_lock. The xdr encoding functions don't > >> appear to be holding i_lock, and may be holding i_mutex, but I > >> haven't looked that far. > > > > I'm still not sure how . . . > > ugh didn't mean to send this reply quite yet, sorry. > > Not sure how we do an unlocked read on a 32-bit machine that doesn't potentially > get the wrong answer. I talked to Bruce about it a bit; nothing jumped out at > us. At worst (?) it seems that if you happened to race on a read at exactly > the 2^32'nd modification, you might go backwards. > > As Bruce says, even if so, maybe "so rare we don't care?" Especially as it requires 2^32 modifications to first be made to the file before there's even the possibility of a high word race on a read and then there's only one increment we could race with before it doesn't chnge again for another 2^32 modifications. Hence, at 1 in 4 billion modifications potentially causing a problem, I'd agree with the "so rare we don't care" assessment. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
