Re: [PATCH net] tcp: make TCP_USER_TIMEOUT accurate for zero window probes

On Fri, Jan 22, 2021 at 9:45 PM Enke Chen [off-list ref] wrote:

Hi, Jakub:

On Fri, Jan 22, 2021 at 06:34:24PM -0800, Jakub Kicinski wrote:

quoted

On Fri, 22 Jan 2021 18:28:23 -0800 Enke Chen wrote:

quoted

Hi, Jakub:

In terms of backporting, this patch should go together with:

    9d9b1ee0b2d1 tcp: fix TCP_USER_TIMEOUT with zero window

As in it:

Fixes: 9d9b1ee0b2d1 tcp: fix TCP_USER_TIMEOUT with zero window

or does it further fix the same issue, so:

Fixes: 9721e709fa68 ("tcp: simplify window probe aborting on USER_TIMEOUT")

?

Let me clarify:

1) 9d9b1ee0b2d1 tcp: fix TCP_USER_TIMEOUT with zero window

   fixes the bug and makes it work.

2) The current patch makes the TCP_USER_TIMEOUT accurate for 0-window probes.
   It's independent.

Patch (2) ("tcp: make TCP_USER_TIMEOUT accurate for zero window
probes") is indeed conceptually independent of (1) but its
implementation depends on the icsk_probes_tstamp field defined in (1),
so AFAICT (2) cannot be backported further back than (1).

Patch (1) fixes a bug in 5.1:
    Fixes: 9721e709fa68 ("tcp: simplify window probe aborting on USER_TIMEOUT")

So probably (1) and (2) should be backported as a pair, and only back
as far as 5.1. (That covers 2 LTS kernels, 5.4 and 5.10, so hopefully
that is good enough.)

neal