Re: [PATCH v2] tcp: fix connection reset due to tw hashdance race.

On Thu, Jun 8, 2023 at 5:59 AM Duan,Muquan [off-list ref] wrote:

Hi, Eric,

Thanks a lot for your explanation!

Even if we add reader lock,  if set the refcnt outside spin_lock()/spin_unlock(), during the interval between spin_unlock() and refcnt_set(),  other cpus will see the tw sock with refcont 0, and validation for refcnt will fail.

A suggestion, before the tw sock is added into ehash table, it has been already used by tw timer and bhash chain, we can firstly add refcnt to 2 before adding two to ehash table,. or add the refcnt one by one for timer, bhash and ehash. This  can avoid the refcont validation failure on other cpus.

This can reduce the frequency of the connection reset issue from 20 min to 180 min for our product,  We may wait quite a long time before the best solution is ready, if this obvious defect is fixed, userland applications can benefit from it.

Looking forward to your opinions!

Again, my opinion is that we need a proper fix, not work arounds.

I will work on this a bit later.

In the meantime you can apply locally your patch if you feel this is
what you want.