From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Serge E. Hallyn" Subject: Re: [PATCH 1/7] Make restore_obj() tolerate a preexisting object in the hash (v2) Date: Fri, 19 Mar 2010 10:21:56 -0500 Message-ID: <20100319152156.GA528@us.ibm.com> References: <1268945512-18814-1-git-send-email-danms@us.ibm.com> <1268945512-18814-2-git-send-email-danms@us.ibm.com> <20100319000434.GA5505@us.ibm.com> <8739zwgxua.fsf@caffeine.danplanet.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <8739zwgxua.fsf-FLMGYpZoEPULwtHQx/6qkW3U47Q5hpJU@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Dan Smith Cc: containers-qjLDD68F18O7TbgM5vRIOg@public.gmane.org, davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org List-Id: containers.vger.kernel.org Quoting Dan Smith (danms-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org): > SH> I don't think this part of the comment is quite right here. The > SH> "on failure this cleans up the object itself" really is for the > SH> ref_drop under IS_ERR() check below. > > SH> The ref_drop here is for the ref taken by obj_new(), which is only > SH> done in this path of course. > > As just discussed on IRC, I couldn't really correct the comment > because the logic it was describing was incorrect. Below is a version > with the correct comment *and* logic :) > > -- > Dan Smith > IBM Linux Technology Center > email: danms-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org > > Make restore_obj() tolerate a preexisting object in the hash (v3) > > ... as long as the pointer is the same as that returned from the restore > function. Also move the compulsory ref_drop() so that it only gets > done if we created the new object. > > The existing object tolerance is important for netdev restore because it > means that I can refer to a peer by its objref instead of needing the > (previously-rejected) veth_peer() function. If this is not acceptable, > then I'll need to keep a separate list of pairs. > > Changes in v3: > - Fix the logic in the case where we need to do an obj_new() and fail, > so that we don't do ref_drop() twice > > Changes in v2: > - Check that the type of the object already in the hash matches that > of the objref header we're reading. > - Add a comment about why and how we might get into this sort of > situation. > > Signed-off-by: Dan Smith Thanks, Dan, for also fixing pre-existing bug :) Acked-by: Serge Hallyn -serge > > diff --git a/checkpoint/objhash.c b/checkpoint/objhash.c > index 7208382..3b360cb 100644 > --- a/checkpoint/objhash.c > +++ b/checkpoint/objhash.c > @@ -1064,17 +1064,32 @@ int restore_obj(struct ckpt_ctx *ctx, struct ckpt_hdr_objref *h) > if (IS_ERR(ptr)) > return PTR_ERR(ptr); > > - if (obj_find_by_objref(ctx, h->objref)) > - obj = ERR_PTR(-EINVAL); > - else > + obj = obj_find_by_objref(ctx, h->objref); > + if (!obj) { > obj = obj_new(ctx, ptr, h->objref, h->objtype); > - /* > - * Drop an extra reference to the object returned by ops->restore: > - * On success, this clears the extra reference taken by obj_new(), > - * and on failure, this cleans up the object itself. > - */ > - ops->ref_drop(ptr, 0); > + /* > + * Drop an extra reference to the object returned by > + * ops->restore to balance the one taken by obj_new() > + */ > + if (!IS_ERR(obj)) > + ops->ref_drop(ptr, 0); > + } else if ((obj->ptr != ptr) || (obj->ops->obj_type != h->objtype)) { > + /* Normally, we expect an object to not already exist > + * in the hash. However, for some special scenarios > + * where we're restoring sets of objects that must be > + * co-allocated (such, as veth netdev pairs) we need > + * to tolerate this case if the second restore returns > + * the correct type and pointer, as specified in the > + * existing object. If either of those don't match, > + * we fail. > + */ > + obj = ERR_PTR(-EINVAL); > + } > + > if (IS_ERR(obj)) { > + /* This releases our final reference on the object > + * returned by ops->restore() > + */ > ops->ref_drop(ptr, 1); > return PTR_ERR(obj); > }