linux-kernel - Re: [PATCH v3 1/7] Fix "x86/alternatives: Lockdep-enforce text_mutex in text

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Date:   Sat, 3 Nov 2018 11:11:20 +0100 (CET)
From:   Jiri Kosina <jikos@...nel.org>
To:     Nadav Amit <namit@...are.com>
cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCH v3 1/7] Fix "x86/alternatives: Lockdep-enforce text_mutex
 in text_poke*()"

On Fri, 2 Nov 2018, Nadav Amit wrote:

> text_mutex is expected to be held before text_poke() is called, but we
> cannot add a lockdep assertion since kgdb does not take it, and instead
> *supposedly* ensures the lock is not taken and will not be acquired by
> any other core while text_poke() is running.
> 
> The reason for the "supposedly" comment is that it is not entirely clear
> that this would be the case if gdb_do_roundup is zero.
> 
> Add a comment to clarify this behavior, and restore the assertions as
> they were before the recent commit.
> 
> This partially reverts commit 9222f606506c ("x86/alternatives:
> Lockdep-enforce text_mutex in text_poke*()")

Alright, what can we do. It's probably better to have this, rather than to 
trying to work this around in kgdb to accomodate the rest of the world.

> Cc: Jiri Kosina <jkosina@...e.cz>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Dave Hansen <dave.hansen@...el.com>
> Fixes: 9222f606506c ("x86/alternatives: Lockdep-enforce text_mutex in text_poke*()")
> Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>
> Tested-by: Masami Hiramatsu <mhiramat@...nel.org>
> Suggested-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Nadav Amit <namit@...are.com>

Acked-by: Jiri Kosina <jkosina@...e.cz>

Thanks,

-- 
Jiri Kosina
SUSE Labs