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

[Steven Rostedt]

On Fri, 24 Apr 2020 14:26:02 -0500
"Christopher M. Riedl" <cmr at informatik.wtf> wrote:

> On Fri Apr 24, 2020 at 9:15 AM, Steven Rostedt wrote:
> > On Thu, 23 Apr 2020 18:21:14 +0200
> > Christophe Leroy <christophe.leroy at c-s.fr> 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.
> >
> > 
> > In fact, there's still BUG_ON()s in my code that I need to convert to
> > WARN_ON() (it was written when BUG_ON() was still acceptable ;-)
> >  
> Figured I'd chime in since I am working on that other series :) The
> BUG_ON()s are _only_ in the init code to set things up to allow a
> temporary mapping for patching a STRICT_RWX kernel later. There's no
> ongoing work to "replace error reporting by BUG_ON()". If that initial
> setup fails we cannot patch under STRICT_KERNEL_RWX at all which imo
> warrants a BUG_ON(). I am still working on v2 of my RFC which does
> return any __patch_instruction() error back to the caller of
> patch_instruction() similar to this patch.


I agree certain locations may warrant a BUG_ON(), but I wouldn't make a
generic operation like patch_instruction() BUG, as it may be used in
cases that do not warrant it (like setting up ftrace).

Deciding to BUG on not based on the return code of patch_instruction()
is the way to go IMO.

-- Steve