netdev - Re: [PATCH v2 net 2/2] net sched actions: decrement module refcount earlier

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Message-ID: <CAM_iQpUPBnWKVHOi2SS6qoeHDPssdj=h03Wg1DLhKk7hbL6_Bg@mail.gmail.com>
Date:   Wed, 19 Apr 2017 10:25:18 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     Wolfgang Bumiller <w.bumiller@...xmox.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v2 net 2/2] net sched actions: decrement module refcount earlier

On Wed, Apr 19, 2017 at 4:32 AM, Jamal Hadi Salim <jhs@...atatu.com> wrote:
> This solves one issue, but I am afraid the issue Cong mentioned is a
> possibility still.
> Lets say user did a replace and tried to also replace the cookie
> in that transaction. The init() succeeds but the cookie allocation
> fails. To be correct we'll have to undo the replace i.e something
> like uninit() which will restore back the old values.
> This is very complex and unnecessary.

It is not complex once we move to RCU completely, replacement
is merely a pointer assignment, rollback is same.

It is necessary too according to the rules of RCU, as I said before, the
current code is broken, we can't modify an existing action with RCU,
we have to make a copy. I do have plan to make actions truly RCU,
but I have to redesign the action API's first.