Re: [PATCH v3 1/7] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()"

From: Thomas Gleixner <tglx@linutronix.de>
To: Nadav Amit <namit@vmware.com>
Cc: Ingo Molnar <mingo@redhat.com>,
	linux-kernel@vger.kernel.org, x86@kernel.org,
	"H. Peter Anvin" <hpa@zytor.com>, Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Jiri Kosina <jkosina@suse.cz>, Andy Lutomirski <luto@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCH v3 1/7] Fix "x86/alternatives: Lockdep-enforce text_mutex in text_poke*()"
Date: Sun, 4 Nov 2018 21:58:20 +0100 (CET)	[thread overview]
Message-ID: <alpine.DEB.2.21.1811042153430.10744@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20181102232946.98461-2-namit@vmware.com>

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.

It restores nothing. It just removes the assertion.

> This partially reverts commit 9222f606506c ("x86/alternatives:
> Lockdep-enforce text_mutex in text_poke*()")

That opens up the same can of worms again, which took us a while to close.

Can we please instead split out the text_poke() code into a helper function
and have two callers:

    text_poke() which contains the assert

    text_poke_kgdb() which does not

Thanks,

	tglx