On Sat, Oct 31, 2015 at 11:54 AM, Jeff Layton <jlay...@poochiereds.net> wrote: > On Sat, 31 Oct 2015 17:31:07 -0400 > Tejun Heo <t...@kernel.org> wrote: ... >> >> > I have asked Chris and Michael to see if they can bisect it down, but >> > it may be a bit before they can get that done. Any insight you might >> > have in the meantime would helpful. >> >> Yeah, I'd love to find out how reproducible the issue is. If the >> problem is rarely reproducible, it might make sense to try >> instrumentation before trying bisection as it *could* be a latent bug >> which has been there all along and bisecting to the commit introducing >> the code wouldn't help us too much. >> > > It seems fairly reproducible, at least on v4.3-rc7 kernels: > > This came about when I asked them to perf test some nfsd patches that I > have queued up. I patched a Fedora 4.3-rc7 kernel and wanted to see > what the perf delta was (with NFSv3, fwiw): > > Patched kernels here: > http://koji.fedoraproject.org/koji/taskinfo?taskID=11598089 > > Unpatched kernels here: > http://koji.fedoraproject.org/koji/buildinfo?buildID=694377 > > Michael was using the SPEC SFS VDI workload to test, and was able to > get the same panic on both kernels. So it does seem to be reproducible. > It might even be possible to tune the VM to make the shrinker fire more > often, which may help tickle this more. > > In any case, I've asked them to try something v4.2-ish and see if it's > reproducible there, and then try v4.1 if it is. I figure anything > earlier is probably not worth testing if it still fails on v4.1. If it > turns out not to be reproducible on those earlier kernels then we can > bisect from there to track it down.
The trick seems to be the NFS thread count: I initially though this was SFS/VDI specific, but when I ratcheted up the thread count to what Michael was using, 256 threads oopses on fio (throughput) benchmarks too. In bisecting kernels, it appeared between 4.2.3-200 and 4.2.5-200 (all the 4.2.4 kernels were bad). Jeff has a lead on this... Chris -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
