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    SubjectRe: [PATCH net] tcp: make TCP_USER_TIMEOUT accurate for zero window probes
    On Fri, Jan 22, 2021 at 9:45 PM Enke Chen <enkechen2020@gmail.com> wrote:
    >
    > Hi, Jakub:
    >
    > On Fri, Jan 22, 2021 at 06:34:24PM -0800, Jakub Kicinski wrote:
    > > On Fri, 22 Jan 2021 18:28:23 -0800 Enke Chen wrote:
    > > > 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

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