On 11/17/13, 1:48 PM, Dave Chinner wrote: > 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. Ok, I'm sold. -Eric > Cheers, > > Dave. > _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
