linux-kernel - Re: [PATCH] uprobes: Improve scalability by reducing the contention on siglock

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Message-ID: <20240801140639.GE4038@redhat.com>
Date: Thu, 1 Aug 2024 16:06:39 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Liao Chang <liaochang1@...wei.com>
Cc: mhiramat@...nel.org, peterz@...radead.org, mingo@...hat.com,
	acme@...nel.org, namhyung@...nel.org, mark.rutland@....com,
	alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
	irogers@...gle.com, adrian.hunter@...el.com,
	kan.liang@...ux.intel.com, linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org
Subject: Re: [PATCH] uprobes: Improve scalability by reducing the contention
 on siglock

On 08/01, Liao Chang wrote:
>
> @@ -2276,22 +2277,25 @@ static void handle_singlestep(struct uprobe_task *utask, struct pt_regs *regs)
>  	int err = 0;
>  
>  	uprobe = utask->active_uprobe;
> -	if (utask->state == UTASK_SSTEP_ACK)
> +	switch (utask->state) {
> +	case UTASK_SSTEP_ACK:
>  		err = arch_uprobe_post_xol(&uprobe->arch, regs);
> -	else if (utask->state == UTASK_SSTEP_TRAPPED)
> +		break;
> +	case UTASK_SSTEP_TRAPPED:
>  		arch_uprobe_abort_xol(&uprobe->arch, regs);
> -	else
> +		fallthrough;
> +	case UTASK_SSTEP_DENY_SIGNAL:
> +		set_tsk_thread_flag(current, TIF_SIGPENDING);
> +		break;
> +	default:
>  		WARN_ON_ONCE(1);
> +	}

Liao, at first glance this change looks "obviously wrong" to me.

But let me read this patch more carefully and reply on weekend,
I am a bit busy right now.

Thanks,

Oleg.