Subject: Re: [PATCH v3 4/8] powerpc/signal64: Remove TM ifdefery in middle of if/else block

From: "Christopher M. Riedl" <[email-masked]>
Date: Sun, 17 Jan 2021 11:16:12 -0600

On Mon Jan 11, 2021 at 7:29 AM CST, Christophe Leroy wrote:
>
>
> Le 09/01/2021 à 04:25, Christopher M. Riedl a écrit :
> > Rework the messy ifdef breaking up the if-else for TM similar to
> > commit f1cf4f93de2f ("powerpc/signal32: Remove ifdefery in middle of if/else").
> > 
> > Unlike that commit for ppc32, the ifdef can't be removed entirely since
> > uc_transact in sigframe depends on CONFIG_PPC_TRANSACTIONAL_MEM.
> > 
> > Signed-off-by: Christopher M. Riedl <[email-masked]>
> > ---
> >   arch/powerpc/kernel/signal_64.c | 17 +++++++----------
> >   1 file changed, 7 insertions(+), 10 deletions(-)
> > 
> > diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
> > index b211a8ea4f6e..dd3787f67a78 100644
> > --- a/arch/powerpc/kernel/signal_64.c
> > +++ b/arch/powerpc/kernel/signal_64.c
> > @@ -710,9 +710,7 @@ SYSCALL_DEFINE0(rt_sigreturn)
> >   	struct pt_regs *regs = current_pt_regs();
> >   	struct ucontext __user *uc = (struct ucontext __user *)regs->gpr[1];
> >   	sigset_t set;
> > -#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
> >   	unsigned long msr;
> > -#endif
> >   
> >   	/* Always make any pending restarted system calls return -EINTR */
> >   	current->restart_block.fn = do_no_restart_syscall;
> > @@ -762,10 +760,12 @@ SYSCALL_DEFINE0(rt_sigreturn)
> >   	 * restore_tm_sigcontexts.
> >   	 */
> >   	regs->msr &= ~MSR_TS_MASK;
> > +#endif
> >   
> >   	if (__get_user(msr, &uc->uc_mcontext.gp_regs[PT_MSR]))
> >   		goto badframe;
>
> This means you are doing that __get_user() even when msr is not used.
> That should be avoided.
>

Thanks, I moved it into the #ifdef block right above it instead for the
next spin.

> >   	if (MSR_TM_ACTIVE(msr)) {
> > +#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
> >   		/* We recheckpoint on return. */
> >   		struct ucontext __user *uc_transact;
> >   
> > @@ -778,9 +778,8 @@ SYSCALL_DEFINE0(rt_sigreturn)
> >   		if (restore_tm_sigcontexts(current, &uc->uc_mcontext,
> >   					   &uc_transact->uc_mcontext))
> >   			goto badframe;
> > -	} else
> >   #endif
> > -	{
> > +	} else {
> >   		/*
> >   		 * Fall through, for non-TM restore
> >   		 *
> > @@ -818,10 +817,8 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
> >   	unsigned long newsp = 0;
> >   	long err = 0;
> >   	struct pt_regs *regs = tsk->thread.regs;
> > -#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
> >   	/* Save the thread's msr before get_tm_stackpointer() changes it */
> > -	unsigned long msr = regs->msr;
> > -#endif
> > +	unsigned long msr __maybe_unused = regs->msr;
>
> I don't thing __maybe_unused() is the right solution.
>
> I think MSR_TM_ACTIVE() should be fixed instead, either by changing it
> into a static inline
> function, or doing something similar to
> https://github.com/linuxppc/linux/commit/05a4ab823983d9136a460b7b5e0d49ee709a6f86
>

Agreed, I'll change MSR_TM_ACTIVE() to reference its argument in the
macro. This keeps it consistent with all the other MSR_TM_* macros in
reg.h. Probably better than changing it to static inline since that
would mean changing all the macros too which seems unecessary.

> >   
> >   	frame = get_sigframe(ksig, tsk, sizeof(*frame), 0);
> >   	if (!access_ok(frame, sizeof(*frame)))
> > @@ -836,8 +833,9 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
> >   	/* Create the ucontext.  */
> >   	err |= __put_user(0, &frame->uc.uc_flags);
> >   	err |= __save_altstack(&frame->uc.uc_stack, regs->gpr[1]);
> > -#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
> > +
> >   	if (MSR_TM_ACTIVE(msr)) {
> > +#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
> >   		/* The ucontext_t passed to userland points to the second
> >   		 * ucontext_t (for transactional state) with its uc_link ptr.
> >   		 */
> > @@ -847,9 +845,8 @@ int handle_rt_signal64(struct ksignal *ksig, sigset_t *set,
> >   					    tsk, ksig->sig, NULL,
> >   					    (unsigned long)ksig->ka.sa.sa_handler,
> >   					    msr);
> > -	} else
> >   #endif
> > -	{
> > +	} else {
> >   		err |= __put_user(0, &frame->uc.uc_link);
> >   		prepare_setup_sigcontext(tsk, 1);
> >   		err |= setup_sigcontext(&frame->uc.uc_mcontext, tsk, ksig->sig,
> > 
>
> Christophe