linux-kernel - Re: [PATCH 1/2] fs/kernel_read_file: add support for duplicate detection

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Message-ID: <CAB=NE6XjXtGmXH-wt_38rKpPPxNoBDOgdNVTsrkD7cOecNG4dg@mail.gmail.com>
Date:   Thu, 25 May 2023 12:32:45 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Linux FS Devel <linux-fsdevel@...r.kernel.org>, hch@....de,
        brauner@...nel.org, david@...hat.com, tglx@...utronix.de,
        patches@...ts.linux.dev, linux-modules@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org, pmladek@...e.com,
        petr.pavlu@...e.com, prarit@...hat.com, lennart@...ttering.net,
        gregkh@...uxfoundation.org, rafael@...nel.org, song@...nel.org,
        lucas.de.marchi@...il.com, lucas.demarchi@...el.com,
        christophe.leroy@...roup.eu, peterz@...radead.org, rppt@...nel.org,
        dave@...olabs.net, willy@...radead.org, vbabka@...e.cz,
        mhocko@...e.com, dave.hansen@...ux.intel.com,
        colin.i.king@...il.com, jim.cromie@...il.com,
        catalin.marinas@....com, jbaron@...mai.com,
        rick.p.edgecombe@...el.com, yujie.liu@...el.com
Subject: Re: [PATCH 1/2] fs/kernel_read_file: add support for duplicate detection

On Thu, May 25, 2023 at 11:50 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> So it would probably improve on those numbers a bit more, but you'd
> still have the fundamental race where *serial* duplicates end up
> always wasting CPU effort and temporary vmalloc space.

The known failed boots are with KASAN with a large number of CPUs, so
the value in
the mitigation would be to help those boot until userspace fixes it
and we have enough
time for propagation. But since it is not a full proof solution, it
may seem like an odd thing
to have in place later and this being lost as odd tribal knowledge.
I'd be in favor of only
applying the mitigation if we really are chasing userspace to fix
this, and we'd be OK
in later removing it after userspace gets this fixed / propagated.

If we're going to have userspace fix this, who is volunteering?

  Luis