linux-kernel - Re: [PATCH v3 0/6] Static calls

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Date:   Fri, 11 Jan 2019 20:39:28 +0100 (CET)
From:   Jiri Kosina <jikos@...nel.org>
To:     hpa@...or.com
cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Nadav Amit <namit@...are.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jason Baron <jbaron@...mai.com>,
        David Laight <David.Laight@...lab.com>,
        Borislav Petkov <bp@...en8.de>,
        Julia Cartwright <julia@...com>, Jessica Yu <jeyu@...nel.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Edward Cree <ecree@...arflare.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH v3 0/6] Static calls

On Fri, 11 Jan 2019, hpa@...or.com wrote:

> I still don't see why can't simply spin in the #BP handler until the 
> patch is complete.

I think this brings us to the already discussed possible deadlock, when 
one CPU#0 is in the middle of text_poke_bp(), CPU#1 is spinning inside 
spin_lock_irq*(&lock) and CPU#2 hits the breakpont while holding that very 
'lock'.

Then we're stuck forever, because CPU#1 will never handle the pending 
sync_core() IPI (it's not NMI).

Or have I misunderstood what you meant?

-- 
Jiri Kosina
SUSE Labs