Re: [PATCH 1/3] powerpc: Properly return error code from do_patch_instruction()

[Steven Rostedt <rostedt@goodmis.org>]

On Fri, 24 Apr 2020 23:37:06 +0530
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:

> >> Le 23/04/2020 à 17:09, Naveen N. Rao a écrit :  
> >> > With STRICT_KERNEL_RWX, we are currently ignoring return value from
> >> > __patch_instruction() in do_patch_instruction(), resulting in the error
> >> > not being propagated back. Fix the same.    
> >> 
> >> Good patch.
> >> 
> >> Be aware that there is ongoing work which tend to wanting to replace 
> >> error reporting by BUG_ON() . See 
> >> https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=166003  
> > 
> > Thanks for the reference. I still believe that WARN_ON() should be used in
> > 99% of the cases, including here. And only do a BUG_ON() when you know
> > there's no recovering from it.  
> 
> I'm not sure if you meant that we should have a WARN_ON() in 
> patch_instruction(), or if it was about the users of 
> patch_instruction(). As you're well aware, ftrace likes to do its own 
> WARN_ON() if any of its operations fail through ftrace_bug(). That was 
> the reason I didn't add anything here.

I'm fine with that too, and better reason not to call BUG_ON(), because I'm
guessing if we crash, we never make it to the ftrace_bug() which reports
information that can be used to debug what went wrong.

-- Steve