Re: [PATCH] powerpc/tm: Don't check for WARN in TM Bad Thing handling

[Michael Neuling <mikey@neuling.org>]

On Thu, 2017-10-12 at 15:45 +1100, Michael Ellerman wrote:
> Currently when we take a TM Bad Thing program check exception, we
> search the bug table to see if the program check was generated by a
> WARN/WARN_ON etc.
>=20
> That makes no sense, the WARN macros use trap instructions, which
> should never generate a TM Bad Thing exception. If they ever did that
> would be a bug and we should oops.
>=20
> We do have some hand-coded bugs in tm.S, using EMIT_BUG_ENTRY, but
> those are all BUGs not WARNs, and they all use trap instructions
> anyway. Almost certainly this check was incorrectly copied from the
> REASON_TRAP handling in the same function.
>=20
> Remove it.
>=20
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

LGTM

Acked-By: Michael Neuling <mikey@neuling.org>

> ---
> =C2=A0arch/powerpc/kernel/traps.c | 9 ++-------
> =C2=A01 file changed, 2 insertions(+), 7 deletions(-)
>=20
> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> index 9ae1924c7d1a..0e4099fef198 100644
> --- a/arch/powerpc/kernel/traps.c
> +++ b/arch/powerpc/kernel/traps.c
> @@ -1337,13 +1337,8 @@ void program_check_exception(struct pt_regs *regs)
> =C2=A0		=C2=A0* -=C2=A0=C2=A0A treclaim is attempted when non transaction=
al.
> =C2=A0		=C2=A0* -=C2=A0=C2=A0A tend is illegally attempted.
> =C2=A0		=C2=A0* -=C2=A0=C2=A0writing a TM SPR when transactional.
> -		=C2=A0*/
> -		if (!user_mode(regs) &&
> -		=C2=A0=C2=A0=C2=A0=C2=A0report_bug(regs->nip, regs) =3D=3D BUG_TRAP_TY=
PE_WARN) {
> -			regs->nip +=3D 4;
> -			goto bail;
> -		}
> -		/* If usermode caused this, it's done something illegal and
> +		=C2=A0*
> +		=C2=A0* If usermode caused this, it's done something illegal and
> =C2=A0		=C2=A0* gets a SIGILL slap on the wrist.=C2=A0=C2=A0We call it an=
 illegal
> =C2=A0		=C2=A0* operand to distinguish from the instruction just being ba=
d
> =C2=A0		=C2=A0* (e.g. executing a 'tend' on a CPU without TM!); it's an