linux-kernel - Re: [PATCH] iov_iter: separate direction from flavour

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Message-ID: <YOI6cES6C0vTS/DU@casper.infradead.org>
Date:   Sun, 4 Jul 2021 23:47:12 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Guenter Roeck <linux@...ck-us.net>, Christoph Hellwig <hch@....de>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        David Sterba <dsterba@...e.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Anton Altaparmakov <anton@...era.com>,
        David Howells <dhowells@...hat.com>,
        Pavel Begunkov <asml.silence@...il.com>
Subject: Re: [PATCH] iov_iter: separate direction from flavour

On Sun, Jul 04, 2021 at 03:44:17PM -0700, Linus Torvalds wrote:
> On Sun, Jul 4, 2021 at 2:47 PM Guenter Roeck <linux@...ck-us.net> wrote:
> >
> > How about the following ?
> >
> >         WARN_ON_ONCE(IS_ENABLED(CONFIG_MMU) && uaccess_kernel());
> 
> Nope, that doesn't work either, because there are no-MMU setups that
> don't make the same mistake no-mmu arm and m68k do.
> 
> Example: xtensa. But afaik also generic-asm/uaccess.h unless the
> architecture overrides something.
> 
> So this literally seems like just an arm/m68k bug.

We could slip:

#ifndef uaccess_user
#define uaccess_user() !uaccess_kernel()
#endif

into asm-generic, switch the test over and then make it arm/m68k's
problem to define uaccess_user() to true?