linux-kernel - Re: Linux 6.2-rc3

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Message-ID: <CANpmjNOmDp_sZgRuks3OZfT015vLwSKcfdFFC=yLGPUNOxnecg@mail.gmail.com>
Date:   Mon, 9 Jan 2023 23:29:54 +0100
From:   Marco Elver <elver@...gle.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <kees@...nel.org>, Jaegeuk Kim <jaegeuk@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Max Filippov <jcmvbkbc@...il.com>
Subject: Re: Linux 6.2-rc3

On Mon, 9 Jan 2023 at 23:18, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
[...]
> > kernel/kcsan/kcsan_test.c: In function '__report_matches':
> > kernel/kcsan/kcsan_test.c:257:1: error: the frame size of 1680 bytes is larger than 1536 bytes
> >
> > Context: CONFIG_SLUB_TINY is enabled with allmodconfig builds.
> > This enables some previously disabled configurations and disables
> > some previously enabled configurations.
>
> I do think that the test code should be a lot more careful about
> random things on stack.
>
> We've had this before with the EXPECT() macros generating *much* too
> much stack space, and it's not ok for test code to violate kernel
> coding standards even if it might be a "odd config that isn't
> realistic".
>
> That function does some odd things, including
>
>         typeof(observed.lines) expect;
>
> WHAT IS THAT TYPE? It turns out that we have
>
>   static struct {
>         spinlock_t lock;
>         int nlines;
>         char lines[3][512];
>   } observed = {
>
> so it's basically a 1.5kB byte array.
>
> And then des
>
>                 char tmp[2][64];
>
> to add some more pressure. So yeah, can't blame the compiler being
> stupid, this is just bad code.
>
> This is all very much a "this needs to be fixed, or the test just
> needs to be removed, because that's not acceptable".
>
> None of this is new, but clearly it was hidden by config issues
> before. Added the guilty parties.

The 1.5kB array is being fixed by
https://lore.kernel.org/lkml/20221231004514.317809-1-jcmvbkbc@gmail.com/
-- I suppose it's fair if you'd like to pull that patch right away, or
wait for the next PR from the xtensa tree (Cc Max).

Thanks,
-- Marco