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    SubjectRe: Possible netlink autobind regression
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    On Wed, Sep 16, 2015 at 8:41 PM, Herbert Xu <herbert@gondor.apana.org.au> wrote:
    > On Thu, Sep 17, 2015 at 11:08:45AM +0800, Herbert Xu wrote:
    >>
    >> Good catch! I think your explanation makes perfect sense. Linus
    >> ran into this previously too after suspend-and-resume.
    >
    > Unfortunately you can't just postpone the setting of portid because
    > once you pass it onto rhashtable the portid must never change while
    > it's in custody.
    >
    > So what I've done is essentially revert my previous fix and instead
    > add a new boolean "bound" to indicate whether the socket has been
    > bound.
    >
    > ---8<---
    > netlink: Fix autobind race condition that leads to zero port ID
    >
    > The commit c0bb07df7d981e4091432754e30c9c720e2c0c78 ("netlink:
    > Reset portid after netlink_insert failure") introduced a race
    > condition where if two threads tried to autobind the same socket
    > one of them may end up with a zero port ID.
    >
    > This patch reverts that commit and instead fixes it by introducing
    > a separte "bound" variable to indicate whether a socket has been
    > bound.
    >
    > Fixes: c0bb07df7d98 ("netlink: Reset portid after netlink_insert failure")
    > Reported-by: Tejun Heo <tj@kernel.org>
    > Reported-by: Linus Torvalds <torvalds@linux-foundation.org>

    We saw similar soft lockup with the one Tejun reported, in our data
    center.


    > Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

    Just one comment below.

    [...]

    > @@ -1285,7 +1287,7 @@ static int netlink_release(struct socket *sock)
    >
    > skb_queue_purge(&sk->sk_write_queue);
    >
    > - if (nlk->portid) {
    > + if (nlk->bound) {
    > struct netlink_notify n = {
    > .net = sock_net(sk),
    > .protocol = sk->sk_protocol,

    This part doesn't look correct, seems it is checking if this is a kernel
    netlink socket rather than if it is bound. But I am not sure...

    Other than this, looks good to me:

    Reviewed-by: Cong Wang <cwang@twopensource.com>


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