Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Thu, 16 Sep 2021 10:03:19 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     =?utf-8?B?546L6LSH?= <yun.wang@linux.alibaba.com>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        "open list:PERFORMANCE EVENTS SUBSYSTEM" 
        <linux-perf-users@vger.kernel.org>,
        "open list:PERFORMANCE EVENTS SUBSYSTEM" 
        <linux-kernel@vger.kernel.org>,
        "open list:BPF (Safe dynamic programs and tools)" 
        <netdev@vger.kernel.org>,
        "open list:BPF (Safe dynamic programs and tools)" 
        <bpf@vger.kernel.org>, jroedel@suse.de, x86@kernel.org
Subject: Re: [PATCH] x86/dumpstack/64: Add guard pages to stack_info
Message-ID: <YUL6R5AH6WNxu5sH@hirez.programming.kicks-ass.net>
References: <ff979a43-045a-dc56-64d1-2c31dd4db381@linux.alibaba.com>
 <20210910153839.GH4323@worktop.programming.kicks-ass.net>
 <f38987a5-dc36-a20d-8c5e-81e8ead5b4dc@linux.alibaba.com>
 <YT8m2B6D2yWc5Umq@hirez.programming.kicks-ass.net>
 <3fb7c51f-696b-da70-1965-1dda9910cb14@linux.alibaba.com>
 <YUB5VchM3a/MiZpX@hirez.programming.kicks-ass.net>
 <3f26f7a2-0a09-056a-3a7a-4795b6723b60@linux.alibaba.com>
 <YUIOgmOfnOqPrE+z@hirez.programming.kicks-ass.net>
 <76de02b7-4d87-4a3a-e4d4-048829749887@linux.alibaba.com>
 <YUL5j/lY0mtx4NMq@hirez.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <YUL5j/lY0mtx4NMq@hirez.programming.kicks-ass.net>
Precedence: bulk

On Thu, Sep 16, 2021 at 10:00:15AM +0200, Peter Zijlstra wrote:
> On Thu, Sep 16, 2021 at 11:47:49AM +0800, 王贇 wrote:
> 
> > I did some debug and found the issue, we are missing:
> > 
> > @@ -122,7 +137,10 @@ static __always_inline bool in_exception_stack(unsigned long *stack, struct stac
> >         info->type      = ep->type;
> >         info->begin     = (unsigned long *)begin;
> >         info->end       = (unsigned long *)end;
> > -       info->next_sp   = (unsigned long *)regs->sp;
> > +
> > +       if (!(ep->type & STACK_TYPE_GUARD))
> > +               info->next_sp   = (unsigned long *)regs->sp;
> > +
> >         return true;
> >  }
> > 
> > as the guard page are not working as real stack I guess?
> 
> Correct, but I thought I put if (type & GUARD) terminators in all paths
> that ended up caring about ->next_sp. Clearly I seem to have missed one
> :/
> 
> Let me try and figure out where that happens.

Oh, I'm an idiot... yes it tries to read regs the stack, but clearly
that won't work for the guard page.