> On April 15, 2017 at 8:20 PM Cong Wang <xiyou.wangc...@gmail.com> wrote: > > > On Fri, Apr 14, 2017 at 2:08 AM, Wolfgang Bumiller > <w.bumil...@proxmox.com> wrote: > > Before I do that - trying to wrap my head around the interdependencies > > here better to be thorough - I noticed that tcf_hash_release() can > > return ACT_P_DELETED. The ACT_P_CREATED case means tcf_hash_create() > > was used, in the other case the tc_action's ref & bind count is bumped > > by tcf_hash_check() and then also decremented by tcf_hash_release() if > > it existed, iow. kept at 1, but not always: It does always happen in > > act_police.c but in other files such as act_bpf.c or act_connmark.c if > > eg. bind is set they return without decrementing, so both ref&bind count > > are bumped when they return - the refcount logic isn't easy to follow > > for a newcomer. Now there are two uses of __tcf_hash_release() in > > act_api.c which check for a return value of ACT_P_DELETED, in which case > > they call module_put(). > > > That's the nasty part... IIRC, Jamal has fixed two bugs on action refcnt'ing. > We really need to clean up the code. > > > So I'm not sure exactly how the module and tc_action counts are related > > (and I usually like to understand my own patches ;-) ). > > > Each action holds a refcnt to its module, each filter holds a refcnt to > its bound or referenced (unbound) action. > > > > Maybe I'm missing something obvious but I'm currently a bit confused as > > to whether the tcf_hash_release() call there is okay, or should have its > > return value checked or should depend on ->init()'s ACT_P_CREATED value > > as well? > > > > I think it's the same? If we have ACT_P_CREATED here, tcf_hash_release() > will return ACT_P_DELETED for sure because the newly created action has > refcnt==1?
Makes sense on the one hand, but for ACT_P_DELETED both ref and bind count need to reach 0, so I'm still concerned that the different behaviors I mentioned above might be problematic if we use ACT_P_CREATED only. (It also means my patches still leak a count - which is probably still better than the previous underflow, but ultimately doesn't satisfy me.) Should I still resend it this way for the record with the Acked-bys? (Since given the fact that with unprivileged containers it's possible to trigger this access and potentially crash the kernel I strongly feel that some version of this should end up in the 4.11 release.)
