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Message-ID: <87imuv977c.fsf@suse.de>
Date: Tue, 30 Apr 2019 11:24:23 +0200
From: Nicolai Stange <nstange@...e.de>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Peter Zijlstra <peterz@...radead.org>,
Nicolai Stange <nstange@...e.de>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>,
"the arch\/x86 maintainers" <x86@...nel.org>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Jiri Kosina <jikos@...nel.org>,
Miroslav Benes <mbenes@...e.cz>,
Petr Mladek <pmladek@...e.com>,
Joe Lawrence <joe.lawrence@...hat.com>,
Shuah Khan <shuah@...nel.org>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Mimi Zohar <zohar@...ux.ibm.com>,
Juergen Gross <jgross@...e.com>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Nayna Jain <nayna@...ux.ibm.com>,
Masahiro Yamada <yamada.masahiro@...ionext.com>,
Andy Lutomirski <luto@...nel.org>,
Joerg Roedel <jroedel@...e.de>,
Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
live-patching@...r.kernel.org,
"open list\:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH 3/4] x86/ftrace: make ftrace_int3_handler() not to skip fops invocation
Steven Rostedt <rostedt@...dmis.org> writes:
> On Mon, 29 Apr 2019 14:38:35 -0700
> Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>
>> On Mon, Apr 29, 2019 at 1:30 PM Steven Rostedt <rostedt@...dmis.org> wrote:
>> >
>> > The update from "call custom_trampoline" to "call iterator_trampoline"
>> > is where we have an issue.
>>
>> So it has never worked. Just tell people that they have two chocies:
>
> The custom call to iterator translation never worked. One option is to
> always call the iterator, and just take the hit. There's another
> solution to to make permanent updates that would handle the live
> patching case, but not for the tracing case. It is more critical for
> live patching than tracing (missed traced function is not as critical
> as running buggy code unexpectedly). I could look to work on that
> instead.
Making the live patching case permanent would disable tracing of live
patched functions though?
For unconditionally calling the iterator: I don't have numbers, but
would expect that always searching through something like 50-70 live
patching ftrace_ops from some hot path will be noticeable.
> If Nicolai has time, perhaps he can try out the method you suggest and
> see if we can move this forward.
You mean making ftrace handle call->call transitions one by one in
non-batch mode, right? Sure, I can do that.
Another question though: is there anything that prevents us from calling
ftrace_ops_list_func() directly from ftrace_int3_handler()? We don't
have parent_ip, but if that is used for reporting only, maybe setting it
to some ftrace_is_in_int3_and_doesnt_now_the_parent() will work?
Graph tracing entries would still be lost, but well...
Thanks,
Nicolai
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