Hi, I'm writing about a problem I'm seeing in a Ceph 0.87 cluster where rbd snap create, rm, etc. are succeeding, but aborting with a non-zero return code because the notify call at the very end of the function (https://github.com/ceph/ceph/blob/v0.87/src/librbd/internal.cc#L468) is hitting an assertion failure (Throttle.cc: 194: FAILED assert(c >= 0)). I did a bit of digging, and found that c is calculated in calc_op_budget (https://github.com/ceph/ceph/blob/v0.87/src/osdc/Objecter.cc#L2453-L2471), which is called in Objecter::_take_op_budget (https://github.com/ceph/ceph/blob/v0.87/src/osdc/Objecter.h#L1597-L1608), but could hypothetically be called again in Objecter::_throttle_op (https://github.com/ceph/ceph/blob/v0.87/src/osdc/Objecter.cc#L2473-L2491), if the first calculation returned 0. From diving into the rd.notify call in IoCtxImpl.notify (https://github.com/ceph/ceph/blob/v0.87/src/librados/IoCtxImpl.cc#L1117), I can see that the call adds an op of type CEPH_OSD_OP_NOTIFY (https://github.com/ceph/ceph/blob/v0.87/src/osdc/Objecter.h#L865), which is defined at https://github.com/ceph/ceph/blob/v0.87/src/include/rados.h#L185. From that, we know that it's the code path at https://github.com/ceph/ceph/blob/v0.87/src/osdc/Objecter.cc#L2463-L2464 that will be taken while calculating the budget, but from there I can't tell where or why there would be extents set on a notify operation. I'm not familiar with the Ceph codebase, so that's the point where I figured I should ask for some advice about this from someone who actually understands this stuff. I also noticed the possibly related issue #9592 (http://tracker.ceph.com/issues/9592), but I'm not totally sure if it's the same issue, it looks like a pretty different reproduction process. I'm not expecting any bugfixes for such an old version of Ceph, but I'd appreciate help just understanding what's different with this particular volume and how to clean it up by hand, and in the unlikely event that this is a problem in the current development version of Ceph, perhaps this can be considered a bug report.
