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Date: Thu, 20 Apr 2017 11:10:48 +0200 From: Daniel Borkmann <daniel@...earbox.net> To: Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org CC: Roi Dayan <roid@...lanox.com>, John Fastabend <john.fastabend@...il.com>, Jamal Hadi Salim <jhs@...atatu.com> Subject: Re: [Patch net-next v4 1/2] net_sched: move the empty tp check from ->destroy() to ->delete() On 04/19/2017 11:21 PM, Cong Wang wrote: > We could have a race condition where in ->classify() path we > dereference tp->root and meanwhile a parallel ->destroy() makes it > a NULL. Daniel cured this bug in commit d936377414fa > ("net, sched: respect rcu grace period on cls destruction"). > > This happens when ->destroy() is called for deleting a filter to > check if we are the last one in tp, this tp is still linked and > visible at that time. The root cause of this problem is the semantic > of ->destroy(), it does two things (for non-force case): > > 1) check if tp is empty > 2) if tp is empty we could really destroy it > > and its caller, if cares, needs to check its return value to see if it > is really destroyed. Therefore we can't unlink tp unless we know it is > empty. > > As suggested by Daniel, we could actually move the test logic to ->delete() > so that we can safely unlink tp after ->delete() tells us the last one is > just deleted and before ->destroy(). > > Fixes: 1e052be69d04 ("net_sched: destroy proto tp when all filters are gone") > Cc: Roi Dayan <roid@...lanox.com> > Cc: Daniel Borkmann <daniel@...earbox.net> > Cc: John Fastabend <john.fastabend@...il.com> > Cc: Jamal Hadi Salim <jhs@...atatu.com> > Signed-off-by: Cong Wang <xiyou.wangcong@...il.com> Acked-by: Daniel Borkmann <daniel@...earbox.net> Thanks!
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