From: Ingo Molnar <mingo@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Eric Dumazet <edumazet@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H . Peter Anvin" <hpa@zytor.com>,
Steven Rostedt <rostedt@goodmis.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Masami Hiramatsu <mhiramat@kernel.org>,
x86@kernel.org, bpf@vger.kernel.org,
Eric Dumazet <eric.dumazet@gmail.com>,
Greg Thelen <gthelen@google.com>,
Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH] x86/alternatives: remove false sharing in poke_int3_handler()
Date: Tue, 25 Mar 2025 09:41:10 +0100 [thread overview]
Message-ID: <Z-JsJruueRgLQ8st@gmail.com> (raw)
In-Reply-To: <20250324113304.GB14944@noisy.programming.kicks-ass.net>
* Peter Zijlstra <peterz@infradead.org> wrote:
> On Mon, Mar 24, 2025 at 08:53:31AM +0100, Eric Dumazet wrote:
>
> > BTW the atomic_cond_read_acquire() part is never called even during my
> > stress test.
>
> Yes, IIRC this is due to text_poke_sync() serializing the state, as that
> does a synchronous IPI broadcast, which by necessity requires all
> previous INT3 handlers to complete.
>
> You can only hit that case if the INT3 remains after step-3 (IOW you're
> actively writing INT3 into the text). This is exceedingly rare.
Might make sense to add a comment for that.
Also, any strong objections against doing this in the namespace:
s/bp_/int3_
?
Half of the code already calls it a variant of 'int3', half of it 'bp',
which I had to think for a couple of seconds goes for breakpoint, not
base pointer ... ;-)
Might as well standardize on int3_ and call it a day?
Thanks,
Ingo
next prev parent reply other threads:[~2025-03-25 8:41 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-03-23 7:25 [PATCH] x86/alternatives: remove false sharing in poke_int3_handler() Eric Dumazet
2025-03-23 21:38 ` Ingo Molnar
2025-03-24 3:59 ` Eric Dumazet
2025-03-24 7:16 ` Ingo Molnar
2025-03-24 7:47 ` Eric Dumazet
2025-03-24 7:53 ` Eric Dumazet
2025-03-24 8:04 ` Ingo Molnar
2025-03-24 11:33 ` Peter Zijlstra
2025-03-25 8:41 ` Ingo Molnar [this message]
2025-03-25 10:30 ` Peter Zijlstra
2025-03-25 11:26 ` Ingo Molnar
2025-03-25 12:31 ` Peter Zijlstra
2025-03-27 20:56 ` Ingo Molnar
2025-03-25 11:36 ` [tip: x86/alternatives] x86/alternatives: Document the text_poke_bp_batch() synchronization rules a bit more tip-bot2 for Peter Zijlstra
2025-03-24 8:02 ` [PATCH] x86/alternatives: remove false sharing in poke_int3_handler() Ingo Molnar
2025-03-24 8:20 ` Eric Dumazet
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