linux-kernel - Re: [PATCH v13 07/14] unwind_user/deferred: Make unwind deferral requests NMI-safe

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Message-ID: <20250714101919.1ea7f323@batman.local.home>
Date: Mon, 14 Jul 2025 10:19:19 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...nel.org>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org, x86@...nel.org,
 Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Josh Poimboeuf <jpoimboe@...nel.org>,
 Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...nel.org>, Namhyung Kim
 <namhyung@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Andrii
 Nakryiko <andrii@...nel.org>, Indu Bhagat <indu.bhagat@...cle.com>, "Jose
 E. Marchesi" <jemarch@....org>, Beau Belgrave <beaub@...ux.microsoft.com>,
 Jens Remus <jremus@...ux.ibm.com>, Linus Torvalds
 <torvalds@...ux-foundation.org>, Andrew Morton <akpm@...ux-foundation.org>,
 Jens Axboe <axboe@...nel.dk>, Florian Weimer <fweimer@...hat.com>, Sam
 James <sam@...too.org>
Subject: Re: [PATCH v13 07/14] unwind_user/deferred: Make unwind deferral
 requests NMI-safe

On Mon, 14 Jul 2025 15:29:36 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> +#ifdef CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG
> +#define UNWIND_NMI_SAFE 1
> +static inline bool try_assign_cnt(struct unwind_task_info *info, u32 cnt)
> +{
> +	u32 zero = 0;
> +	return try_cmpxchg(&info->id.cnt, &zero, cnt);
> +}
> +static inline bool test_and_set_pending(struct unwind_task_info *info)
> +{
> +	return info->pending || cmpxchg_local(&info->pending, 0, 1);
> +}
> +#el

Patch 10 moves the pending bit into the unwind_mask as it needs to be
in sync with the different tracer requests. I'm not sure how this
change will interact with that.

-- Steve