On Fri, 24 Apr 2020 14:26:02 -0500
"Christopher M. Riedl" [off-list ref] wrote:

On Fri Apr 24, 2020 at 9:15 AM, Steven Rostedt wrote:

quoted

On Thu, 23 Apr 2020 18:21:14 +0200
Christophe Leroy [off-list ref] wrote:

  

quoted

Le 23/04/2020 à 17:09, Naveen N. Rao a écrit :  

quoted

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