From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Smith Subject: Re: [PATCH 1/7] Make restore_obj() tolerate a preexisting object in the hash (v2) Date: Fri, 19 Mar 2010 08:01:01 -0700 Message-ID: <8739zwgxua.fsf@caffeine.danplanet.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> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20100319000434.GA5505-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org> (Serge E. Hallyn's message of "Thu\, 18 Mar 2010 19\:04\:34 -0500") 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: "Serge E. Hallyn" Cc: containers-qjLDD68F18O7TbgM5vRIOg@public.gmane.org, davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org List-Id: containers.vger.kernel.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 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); }