linux-kernel - Re: [PATCH v2 2/2] uprobes: Remove the spinlock within handle

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Message-ID: <20240812112929.GB11656@redhat.com>
Date: Mon, 12 Aug 2024 13:29:29 +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, andrii@...nel.org, rostedt@...dmis.org,
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH v2 2/2] uprobes: Remove the spinlock within
 handle_singlestep()

On 08/09, Liao Chang wrote:
>
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -75,6 +75,7 @@ struct uprobe_task {
>  
>  	struct uprobe			*active_uprobe;
>  	unsigned long			xol_vaddr;
> +	bool				deny_signal;

Ack, but... I can't believe I am arguing with the naming ;)
Can we have a better name for this flag?

	utask->signal_denied ?
	utask->restore_sigpending ?

or just

	utask->sigpending ?

utask->deny_signal looks as if handle_singlestep/whatever should
"deny" the pending signal cleared by uprobe_deny_signal(), while
it fact it should restore TIF_SIGPENDING.

Oleg.

>  
>  	struct return_instance		*return_instances;
>  	unsigned int			depth;
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 76a51a1f51e2..77934fbd1370 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1979,6 +1979,7 @@ bool uprobe_deny_signal(void)
>  	WARN_ON_ONCE(utask->state != UTASK_SSTEP);
>  
>  	if (task_sigpending(t)) {
> +		utask->deny_signal = true;
>  		clear_tsk_thread_flag(t, TIF_SIGPENDING);
>  
>  		if (__fatal_signal_pending(t) || arch_uprobe_xol_was_trapped(t)) {
> @@ -2288,9 +2289,10 @@ static void handle_singlestep(struct uprobe_task *utask, struct pt_regs *regs)
>  	utask->state = UTASK_RUNNING;
>  	xol_free_insn_slot(current);
>  
> -	spin_lock_irq(&current->sighand->siglock);
> -	recalc_sigpending(); /* see uprobe_deny_signal() */
> -	spin_unlock_irq(&current->sighand->siglock);
> +	if (utask->deny_signal) {
> +		set_thread_flag(TIF_SIGPENDING);
> +		utask->deny_signal = false;
> +	}
>  
>  	if (unlikely(err)) {
>  		uprobe_warn(current, "execute the probed insn, sending SIGILL.");
> -- 
> 2.34.1
>