linux-kernel - Re: regression from your recent change to x86's copy_user_handle

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Message-ID: <CA+55aFwKz+5Z7XrRBV5XkA2bmYhCRdWLdCafc78=+9WQ4mqJug@mail.gmail.com>
Date:	Thu, 23 Apr 2015 08:52:20 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Jan Beulich <JBeulich@...e.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: regression from your recent change to x86's copy_user_handle_tail()

On Thu, Apr 23, 2015 at 8:43 AM, Jan Beulich <JBeulich@...e.com> wrote:
>>
>> Did you have a test-case for this? I guess we're talking odd ftrace
>> uses or kgdb?
>
> I'm afraid not one you'd like - we've seen ftrace initialization fail for
> quite some time on our Xen kernels, but in a way only affecting
> ftrace itself. Said change converted that failure to an oops

So if you have a reproducer and can test the suggested one-liner patch
for it, I don't really are whether I personally consider your odd
test-case "sane" or not ;)

I think the __probe_kernel_write() code path is kind of odd and nasty,
but I think your point was good, and I think the one-liner makes
conceptual sense. So I don't have any problem applying that patch, and
even marking it for stable. I just want to make sure that it gets
tested on that odd (crazy) case, just to validate that there's nothing
else going on.

So I don't need some test-case for *me* to test and care about. I just
want that patch validated so that I can happily commit it with a
tested-by..

                       Linus
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