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

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 :

quoted

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 <redacted>
---
  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.

quoted

  	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.

quoted

  
  	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