On Fri, 24 Apr 2020 23:37:06 +0530
"Naveen N. Rao" [off-list ref] wrote:

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

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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