linux-kernel - Re: [PATCH -v5 00/17] Rewrite x86/ftrace to use text

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Message-ID: <20191125123245.5ae9cb60@gandalf.local.home>
Date:   Mon, 25 Nov 2019 12:32:45 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, bristot@...hat.com,
        jbaron@...mai.com, torvalds@...ux-foundation.org,
        tglx@...utronix.de, mingo@...nel.org, namit@...are.com,
        hpa@...or.com, luto@...nel.org, ard.biesheuvel@...aro.org,
        jpoimboe@...hat.com, jeyu@...nel.org, alexei.starovoitov@...il.com
Subject: Re: [PATCH -v5 00/17] Rewrite x86/ftrace to use text_poke (and
 more)

On Mon, 25 Nov 2019 12:55:34 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> void text_poke_bp_batch(struct text_poke_loc *tp, unsigned int nr_entries)
> ...
>         on_each_cpu(do_sync_core, NULL, 1);
>         /*
>          * sync_core() implies an smp_mb() and orders this store against
>          * the writing of the new instruction.
>          */
>         bp_patching.vec = NULL;
>         bp_patching.nr_entries = 0;
> }
> -----
> 
> I think the "on_each_cpu(do_sync_core, NULL, 1);" can sync the pipeline
> but doesn't ensure all ongoing int3 handling is done. Thus, we may need a

How does it not ensure all ongoing int3 handling is done? int3 is done
with interrupts disabled, and the on_each_cpu() requires all CPUs to
have had their interrupts enabled, thus int3 handling should be
completed. Perhaps we need another sync core?

	on_each_cpu(do_sync_core, NULL, 1);
	bp_patching.nr_entries = 0;
	on_each_cpu(do_sync_core, NULL, 1);
	bp_patching.vec = NULL;

?

-- Steve


> bigger wait in between bp_patching.nr_entries = 0 and bp_patching.vec = NULL;