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Message-ID: <20190318172024.GB23521@redhat.com>
Date: Mon, 18 Mar 2019 18:20:24 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Sudeep Holla <sudeep.holla@....com>
Cc: x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
Paul Mackerras <paulus@...ba.org>,
Michael Ellerman <mpe@...erman.id.au>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
Richard Weinberger <richard@....at>, jdike@...toit.com,
Steve Capper <Steve.Capper@....com>,
Haibo Xu <haibo.xu@....com>, Bin Lu <bin.lu@....com>,
Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v2 4/6] powerpc: use common ptrace_syscall_enter hook to
handle _TIF_SYSCALL_EMU
On 03/18, Sudeep Holla wrote:
>
> --- a/arch/powerpc/kernel/ptrace.c
> +++ b/arch/powerpc/kernel/ptrace.c
> @@ -3278,35 +3278,29 @@ long do_syscall_trace_enter(struct pt_regs *regs)
>
> user_exit();
>
> - flags = READ_ONCE(current_thread_info()->flags) &
> - (_TIF_SYSCALL_EMU | _TIF_SYSCALL_TRACE);
> -
> - if (flags) {
> - int rc = tracehook_report_syscall_entry(regs);
> + if (unlikely(ptrace_syscall_enter(regs))) {
> + /*
> + * 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 registers, so we don't goto the skip
> + * label below.
> + */
> + return -1;
> + }
>
> - if (unlikely(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 registers, so we don't goto
> - * the skip label below.
> - */
> - return -1;
> - }
> + flags = READ_ONCE(current_thread_info()->flags) & _TIF_SYSCALL_TRACE;
Why do we need READ_ONCE() with this change?
And now that we change a single bit "flags" doesn't look like a good name.
Again, to me this patch just makes the code look worse. Honestly, I don't
think that the new (badly named) ptrace_syscall_enter() hook makes any sense.
Oleg.
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