Re: [GIT pull] sched/core for v5.16-rc1

[Linus Torvalds]

On Sun, Oct 31, 2021 at 6:16 PM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>
>  - Make wchan() more robust and work with all kind of unwinders by
>    enforcing that the task stays blocked while unwinding is in progress.

Ugh. This not-very-important data is protected by a rather core lock.

Is this yet another example of "unwinding is so fragile that it can
screw up unless we take a lock that is seriously overkill for a not
very important operation"?

Unwinders that need locks because they can do bad things if they are
working on unstable data are EVIL and WRONG.

I guess I don't care too much about the pi_lock, and the actual
unwinding is hopefully done on tasks that don't care about it, but
this smells suspicious to me.

Why is that "stable wchan" so magically important?

               Linus