Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 17 Dec 2018 12:27:31 +0100
From:   Oleg Nesterov <oleg@redhat.com>
To:     "Dmitry V. Levin" <ldv@altlinux.org>
Cc:     Michael Ellerman <mpe@ellerman.id.au>,
        linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] powerpc/ptrace: cleanup do_syscall_trace_enter
Message-ID: <20181217112730.GA25465@redhat.com>
References: <87efbe166y.fsf@concordia.ellerman.id.au>
 <20181203031823.GE11573@altlinux.org>
 <20181207011946.GA18558@altlinux.org>
 <87y391k2tq.fsf@concordia.ellerman.id.au>
 <20181207154255.GA28964@altlinux.org>
 <20181207155605.GB28964@altlinux.org>
 <20181207185226.GB31278@altlinux.org>
 <20181210132806.GA4177@redhat.com>
 <20181210133655.GH11942@altlinux.org>
 <20181216172828.GA25359@altlinux.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20181216172828.GA25359@altlinux.org>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 12/16, Dmitry V. Levin wrote:
>
>  long do_syscall_trace_enter(struct pt_regs *regs)
>  {
> +	u32 cached_flags;
> +
>  	user_exit();
>  
> -	if (test_thread_flag(TIF_SYSCALL_EMU)) {
> -		/*
> -		 * A nonzero return code from tracehook_report_syscall_entry()
> -		 * tells us to prevent the syscall execution, but we are not
> -		 * going to execute it anyway.
> -		 *
> -		 * Returning -1 will skip the syscall execution. We want to
> -		 * avoid clobbering any register also, thus, not 'gotoing'
> -		 * skip label.
> -		 */
> -		if (tracehook_report_syscall_entry(regs))
> -			;
> -		return -1;
> -	}
> +	cached_flags = READ_ONCE(current_thread_info()->flags) &
> +		       (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE);
>  
> -	/*
> -	 * The tracer may decide to abort the syscall, if so tracehook
> -	 * will return !0. Note that the tracer may also just change
> -	 * regs->gpr[0] to an invalid syscall number, that is handled
> -	 * below on the exit path.
> -	 */
> -	if (test_thread_flag(TIF_SYSCALL_TRACE) &&
> -	    tracehook_report_syscall_entry(regs))
> -		goto skip;
> +	if (cached_flags) {
> +		int rc = tracehook_report_syscall_entry(regs);
> +
> +		if (unlikely(cached_flags & _TIF_SYSCALL_EMU)) {
> +			/*
> +			 * A nonzero return code from
> +			 * tracehook_report_syscall_entry() tells us
> +			 * to prevent the syscall execution, but
> +			 * we are not going to execute it anyway.
> +			 *
> +			 * Returning -1 will skip the syscall execution.
> +			 * We want to avoid clobbering any register also,
> +			 * thus, not 'gotoing' skip label.
> +			 */
> +			return -1;
> +		}
> +
> +		if (rc) {
> +			/*
> +			 * The tracer decided to abort the syscall.
> +			 * Note that the tracer may also just change
> +			 * regs->gpr[0] to an invalid syscall number,
> +			 * that is handled below on the exit path.
> +			 */
> +			goto skip;
> +		}
> +	}

Looks good to me,

Oleg.