On Thu, Dec 14, 2017 at 08:08:53AM -0500, Benjamin Coddington wrote: > > On 13 Dec 2017, at 12:18, J. Bruce Fields wrote: > > > On Fri, Dec 08, 2017 at 05:16:26PM -0500, J. Bruce Fields wrote: > >> Last year Christoph noticed a bug that could result in a file being > >> unnecessarily sillyrenamed after O_DIRECT writes get ENOSPC: > >> > >> http://lkml.kernel.org/r/20160616150146.GA14015@xxxxxxxxxxxxx > >> > >> It's reproduceable on upstream, over v3 or v4. > >> > >> I looked into it some more, and it seems to reproduce whenever a write > >> system call results in multiple WRITE calls, only some of which receive > >> ENOSPC. I think that's resulting in a leak of the wb_kref on some > >> nfs_pages (possibly the ones corresponding to the ENOSPC failures?). > >> Those nfs_pages in turn hold references on nfs_{lock,open}_contexts. So > >> a "rm" on the client (even after the file is closed) results in a > >> sillyrename. > >> > >> I'll keep looking at this, but the relevant code is pretty opaque to me > >> so far. Any ideas welcomed. > > > > Actually it looks like a leak of dreq->io_count? That prevents commits > > from being sent (which I'm also seeing in network traces--the succesfull > > WRITEs are unstable but never get committed), which means > > nfs_direct_commit_complete() is never called, and the reference taken on > > wb_kref in the request_commit case of nfs_direct_write_completion is > > never put. > > This sounds to me like the problem Scott's working - he sent a patch > yesterday "nfs/pnfs: fix nfs_direct_req ref leak when i/o falls back to the > mds". > > I think the the rule should be that once we call > nfs_pgio_completion_ops->init_hdr, we have to finish with ->completion. > However, there are some paths where that is not the case. Yes, I wondered about that.... Unfortunately after some more tests now I was think I was wrong, the dreq_get()s and put()s are balanced and the bug is somewhere else--in the case of my particular reproducer. Argh. But yes I can easily believe there could be a leak there. --b. > > The callgraph in between nfs_pgheader_init() and nfs_initiate_pgio() in > nfs_generic_pg_pgios() for this case might show where we're bailing out > early. -- 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
