On Tue, Aug 14, 2012 at 9:45 PM, Myklebust, Trond <Trond.Myklebust@xxxxxxxxxx> wrote: > On Tue, 2012-08-14 at 10:48 +0300, Benny Halevy wrote: >> On 2012-08-09 18:39, Myklebust, Trond wrote: >> > On Thu, 2012-08-09 at 23:01 +0800, Peng Tao wrote: >> >> On Thu, Aug 9, 2012 at 10:36 PM, Myklebust, Trond >> >> <Trond.Myklebust@xxxxxxxxxx> wrote: >> >>> On Thu, 2012-08-09 at 22:30 +0800, Peng Tao wrote: >> >>>> On Thu, Aug 9, 2012 at 4:21 AM, Trond Myklebust >> >>>> <Trond.Myklebust@xxxxxxxxxx> wrote: >> >>>>> Ever since commit 0a57cdac3f (NFSv4.1 send layoutreturn to fence >> >>>>> disconnected data server) we've been sending layoutreturn calls >> >>>>> while there is potentially still outstanding I/O to the data >> >>>>> servers. The reason we do this is to avoid races between replayed >> >>>>> writes to the MDS and the original writes to the DS. >> >>>>> >> >>>>> When this happens, the BUG_ON() in nfs4_layoutreturn_done can >> >>>>> be triggered because it assumes that we would never call >> >>>>> layoutreturn without knowing that all I/O to the DS is >> >>>>> finished. The fix is to remove the BUG_ON() now that the >> >>>>> assumptions behind the test are obsolete. >> >>>>> >> >>>> Isn't MDS supposed to recall the layout if races are possible between >> >>>> outstanding write-to-DS and write-through-MDS? >> >>> >> >>> Where do you read that in RFC5661? >> >>> >> >> That's my (maybe mis-)understanding of how server works... But looking >> >> at rfc5661 section 18.44.3. layoutreturn implementation. >> >> " >> >> After this call, >> >> the client MUST NOT use the returned layout(s) and the associated >> >> storage protocol to access the file data. >> >> " >> >> And given commit 0a57cdac3f, client is using the layout even after >> >> layoutreturn, which IMHO is a violation of rfc5661. >> > >> > No. It is using the layoutreturn to tell the MDS to fence off I/O to a >> > data server that is not responding. It isn't attempting to use the >> > layout after the layoutreturn: the whole point is that we are attempting >> > write-through-MDS after the attempt to write through the DS timed out. >> > >> >> I hear you, but this use case is valid after a time out / disconnect >> (which will translate to PNFS_OSD_ERR_UNREACHABLE for the objects layout) >> In other cases, I/Os to the DS might obviously be in flight and the BUG_ON >> indicates that. >> >> IMO, the right way to implement that is to initially mark the lsegs invalid >> and increment plh_block_lgets, as we do today in _pnfs_return_layout >> but actually send the layout return only when the last segment is dereferenced. > > This is what we do for object and block layout types, so your > objects-specific objection is unfounded. > object layout is also doing layout return on IO error (commit fe0fe83585f8). And it doesn't take care of draining concurrent in-flight IO. I guess that's why Boaz saw the same BUG_ON. -- Thanks, Tao -- 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
