linux-kernel - Re: [PATCH v10 04/14] unwind_user/deferred: Add unwind_deferred

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Message-ID: <20250618140111.GP1613376@noisy.programming.kicks-ass.net>
Date: Wed, 18 Jun 2025 16:01:11 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: 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>
Subject: Re: [PATCH v10 04/14] unwind_user/deferred: Add
 unwind_deferred_trace()

On Tue, Jun 10, 2025 at 08:54:25PM -0400, Steven Rostedt wrote:

> +#define UNWIND_MAX_ENTRIES 512

The reason this is 512 is so that you end up with a whole page below?

> +int unwind_deferred_trace(struct unwind_stacktrace *trace)
> +{
> +	struct unwind_task_info *info = &current->unwind_info;
> +
> +	/* Should always be called from faultable context */
> +	might_fault();
> +
> +	if (current->flags & PF_EXITING)
> +		return -EINVAL;
> +
> +	if (!info->entries) {
> +		info->entries = kmalloc_array(UNWIND_MAX_ENTRIES, sizeof(long),
> +					      GFP_KERNEL);