linux-kernel - Re: [PATCH] sched/tracing: append prev

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Message-ID: <056e9bb0d0e3fc20572d42db7386face1d0665d6.camel@fb.com>
Date:   Fri, 22 Apr 2022 17:22:20 +0000
From:   Delyan Kratunov <delyank@...com>
To:     "peterz@...radead.org" <peterz@...radead.org>
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Subject: Re: [PATCH] sched/tracing: append prev_state to tp args instead

On Fri, 2022-04-22 at 13:09 +0200, Peter Zijlstra wrote:
> And on the other hand; those users need to be fixed anyway, right?
> Accessing prev->__state is equally broken.

The users that access prev->__state would most likely have to be fixed, for sure.

However, not all users access prev->__state. `offcputime` for example just takes a
stack trace and associates it with the switched out task. This kind of user
would continue working with the proposed patch.

> If bpf wants to ride on them, it needs to suffer the pain of doing so.

Sure, I'm just advocating for a fairly trivial patch to avoid some of the suffering,
hopefully without being a burden to development. If that's not the case, then it's a
clear no-go.