On 12/21/2016 07:51 PM, Cong Wang wrote:
On Wed, Dec 21, 2016 at 9:04 AM, Daniel Borkmann <dan...@iogearbox.net> wrote:What happens is that in tc_ctl_tfilter(), thread A allocates a new tp, initializes it, sets tp_created to 1, and calls into tp->ops->change() with it. In that classifier callback we had to unlock/lock the rtnl mutex and returned with -EAGAIN. One reason why we need to drop there is, for example, that we need to request an action module to be loaded.Excellent catch! But why do we have to replay the request here? Shouldn't we just return EAGAIN to user-space and let user-space decide to retry or not? Replaying is the root of the evil here.
Right, this behavior is already pretty old (2005), see history
tree 8d7c694553dc ("[PKT_SCHED]: act_api.c: drop rtnl for loading
modules") and 437293de63d8 ("[PKT_SCHED]: cls_api.c: drop rtnl
for loading modules"), some binaries could rely on that behavior
in one way or another I'd presume.
