On Wed, Jun 4, 2014 at 3:39 AM, NeilBrown <neilb@xxxxxxx> wrote: > On Sat, 31 May 2014 08:13:58 +1000 NeilBrown <neilb@xxxxxxx> wrote: > >> On Fri, 30 May 2014 17:55:23 -0400 "J. Bruce Fields" <bfields@xxxxxxxxxxxx> >> wrote: >> >> > On Fri, May 30, 2014 at 01:44:42PM +1000, NeilBrown wrote: >> > > On Thu, 29 May 2014 20:44:23 -0400 "J. Bruce Fields" <bfields@xxxxxxxxxxxx> >> > > wrote: >> > > >> > > > Yes, it's a known server bug. >> > > > >> > > > As a first attempt I was thinking of just sticking a timestamp in struct >> > > > inode to record the time of the most recent conflicting access and deny >> > > > delegations if the timestamp is too recent, for some definition of too >> > > > recent. >> > > > >> > > >> > > Hmmm... I'll have a look next week and see what I can come up with. >> > >> > Thanks! >> > >> > If we didn't think it was worth another struct inode field, we could >> > probably get away with global state. Even just refusing to give out any >> > delegations for a few seconds after any delegation break would be enough >> > to fix this bug. >> > >> > Or you could make it a little less harsh with a small hash table: "don't >> > give out a delegation on any inode whose inode number hashes to X for a >> > few seconds." >> >> I was thinking of using a bloom filter - or possibly two. >> - avoid handing out delegations if either bloom filter reports a match >> - when reclaiming a delegation add the inode to the second bloom filter >> - every so-often zero-out the older filter and swap them. >> >> Might be a bit of overkill, but I won't know until I implement it. >> > > Below is my suggestion. It seems easy enough. It even works. > > However it does raise an issue with the NFS client. > > NFS performs a silly-rename as an 'asynchronous' operation. One consequence > of this is that NFS4ERR_DELAY always results in a delay of > NFS4_POLL_RETRY_MAX (15*HZ), where as sync requests use an exponential scale > from _MIN to _MAX. > > So in my test case there is always a 15second delay: > - try to silly-rename > - get NFS4ERR_DELAY > - server reclaim delegation > - 15 seconds passes > - retry silly-rename - it works. > > I hacked the NFS server to store a timeout in 'struct nfs_renamedata', and > use the same exponential retry pattern and the 15 seconds (obviously) > disappeared. > > Trond: would you accept a patch which did that more generally? e.g. pass a > timeout pointer to nfs4_async_handle_error() and various *_done function pass > a pointer to a field in their calldata? It depends. If we're touching nfs4_async_handle_error, then I think we should also convert nfs4_async_handle_error to use the same "struct nfs4_exception" argument that we use for the synchronous case so that we can share a bit more code. -- Trond Myklebust Linux NFS client maintainer, PrimaryData trond.myklebust@xxxxxxxxxxxxxxx -- 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
