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Date:   Mon, 5 Sep 2022 13:26:47 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
        x86@kernel.org, Tim Chen <tim.c.chen@linux.intel.com>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        Andrew Cooper <Andrew.Cooper3@citrix.com>,
        Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
        Johannes Wikner <kwikner@ethz.ch>,
        Alyssa Milburn <alyssa.milburn@linux.intel.com>,
        Jann Horn <jannh@google.com>, "H.J. Lu" <hjl.tools@gmail.com>,
        Joao Moreira <joao.moreira@intel.com>,
        Joseph Nuzman <joseph.nuzman@intel.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Juergen Gross <jgross@suse.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        K Prateek Nayak <kprateek.nayak@amd.com>,
        Eric Dumazet <edumazet@google.com>
Subject: Re: [PATCH v2 37/59] x86/putuser: Provide room for padding
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On Mon, Sep 05, 2022 at 09:16:43AM +0200, Peter Zijlstra wrote:
> On Sat, Sep 03, 2022 at 10:26:45AM -0700, Linus Torvalds wrote:
> > On Fri, Sep 2, 2022 at 2:46 PM Linus Torvalds
> > <torvalds@linux-foundation.org> wrote:
> > >
> > > Hmm. It doesn't look too horrible, but yeah, fi it still ends up
> > > getting the same padding overhead I'm not sure it ends up really
> > > mattering.
> > 
> > Oh, and I think it's buggy anyway.
> > 
> > If there are any tail-calls to a leaf function, the tracking now gets
> > out of whack. So it's no longer a "don't bother counting the last
> > level", now it ends up being a "count got off by one".
> 
> See validate_sibling_call(), it too calls validate_call().
> 
> (Although prehaps I should go s/sibling/tail/ on all that for clarity)

Ah, no, you're right and I needed more wake-up juice.