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Date:   Thu, 10 Feb 2022 23:37:06 +0800
From:   Jisheng Zhang <jszhang@kernel.org>
To:     Changbin Du <changbin.du@gmail.com>
Cc:     Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] riscv: fix oops caused by irq on/off tracer
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On Thu, Feb 10, 2022 at 11:27:21PM +0800, Jisheng Zhang wrote:
> On Thu, Feb 10, 2022 at 09:37:58PM +0800, Changbin Du wrote:
> > On Thu, Feb 10, 2022 at 01:32:59AM +0800, Jisheng Zhang wrote:
> > [snip]
> > > Hi Changbin,
> > > 
> > > I read the code and find that current riscv frame records during
> > > exception isn't as completed as other architectures. riscv only
> > > records frames from the ret_from_exception(). If we add completed
> > What do you mean for 'record'?
> > 
> 
> stack frame record.
> 
> > > frame records as other arch do, then the issue you saw can also
> > > be fixed at the same time.
> > > 
> > I don't think so. The problem is __builtin_return_address(1) trigger page fault
> > here.
> 
> There's misunderstanding here. I interpret this bug as incomplete
> stackframes.
> 
> This is current riscv stackframe during exception:
> 
> high
>  	----------------
> top	|		|  <- ret_from_exception
> 	----------------
> 	|		|  <- trace_hardirqs_on
> 	-----------------
> low

sorry, the "top" is wrongly placed.
 high
  	----------------
 	|		|  <- ret_from_exception
 	----------------
 	|		|  <- trace_hardirqs_on
 	-----------------
top

 low


> 
> As you said, the CALLER_ADDR1 a.k.a __builtin_return_address(1) needs
> at least two parent call frames. 
> 
> If we complete the stackframes during exception as other arch does:
> 
> high
>  	----------------
> top	|		|  <- the synthetic stackframe from the interrupted point
>  	----------------
> 	      .....	      
>         ----------------
> 	|		|  <- ret_from_exception
> 	----------------
> 	|		|  <- trace_hardirqs_on
> 	-----------------
> low

ditto

> 
> 
> Then we meet the "at least two parent call frames" requirement. IOW, my
> solution solve the problem from the entry.S side. One of the advantages
> would be we let interrupted point show up in dump_stack() as other arch
> do. What I'm not sure is whether it's safe to do so now since rc3 is
> released.
>