linux-kernel - Re: [PATCH v4 43/45] namei: initialize parameters passed to step

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Message-ID: <YsNVyLxrNRFpufn8@ZenIV>
Date:   Mon, 4 Jul 2022 22:04:08 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Alexander Potapenko <glider@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Christoph Hellwig <hch@....de>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Ingo Molnar <mingo@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Kees Cook <keescook@...omium.org>,
        Marco Elver <elver@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Matthew Wilcox <willy@...radead.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Pekka Enberg <penberg@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux-MM <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        Vitaly Buka <vitalybuka@...gle.com>,
        linux-toolchains <linux-toolchains@...r.kernel.org>
Subject: Re: [PATCH v4 43/45] namei: initialize parameters passed to
 step_into()

On Mon, Jul 04, 2022 at 01:51:16PM -0700, Linus Torvalds wrote:
> On Mon, Jul 4, 2022 at 1:46 PM Al Viro <viro@...iv.linux.org.uk> wrote:
> >
> > Why is that a problem?  It could have been moved to another parent,
> > but so it could after we'd crossed to the mounted and we wouldn't have
> > noticed (or cared).
> 
> Yeah, see my other email.
> 
> I agree that it might be a "we don't actually care" situation, where
> all we care about that the name was valid at one point (when we picked
> up that sequence point). So maybe we don't care about closing it.
> 
> But even if so, I think it might warrant a comment, because I still
> feel like we're basically "throwing away" our previous sequence point
> information without ever checking it.
> 
> Maybe all we ever care about is basically "this sequence point
> protects the dentry inode pointer for the next lookup", and when it
> comes to mount points that ends up being immaterial.

	There is a problem, actually, but it's in a different place...
OK, let me try to write something resembling a formal proof and see
what falls out.