powerpc: fix double syscall restarts

Make sigreturn zero regs->trap, make do_signal() do the same on all
paths.  As it is, signal interrupting e.g. read() from fd 512 (==
ERESTARTSYS) with another signal getting unblocked when the first
handler finishes will lead to restart one insn earlier than it ought
to.  Same for multiple signals with in-kernel handlers interrupting
that sucker at the same time.  Same for multiple signals of any kind
interrupting that sucker on 64bit...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Acked-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/powerpc/kernel/signal.c

@@ -138,6 +138,7 @@ static int do_signal_pending(sigset_t *oldset, struct pt_regs *regs)
 			ti->local_flags &= ~_TLF_RESTORE_SIGMASK;
 			sigprocmask(SIG_SETMASK, &current->saved_sigmask, NULL);
 		}
+		regs->trap = 0;
 		return 0;               /* no signals delivered */
 	}
 
@@ -164,6 +165,7 @@ static int do_signal_pending(sigset_t *oldset, struct pt_regs *regs)
 		ret = handle_rt_signal64(signr, &ka, &info, oldset, regs);
 	}
 
+	regs->trap = 0;
 	if (ret) {
 		spin_lock_irq(&current->sighand->siglock);
 		sigorsets(&current->blocked, &current->blocked,

arch/powerpc/kernel/signal_32.c

@@ -511,6 +511,7 @@ static long restore_user_regs(struct pt_regs *regs,
 	if (!sig)
 		save_r2 = (unsigned int)regs->gpr[2];
 	err = restore_general_regs(regs, sr);
+	regs->trap = 0;
 	err |= __get_user(msr, &sr->mc_gregs[PT_MSR]);
 	if (!sig)
 		regs->gpr[2] = (unsigned long) save_r2;
@@ -884,7 +885,6 @@ int handle_rt_signal32(unsigned long sig, struct k_sigaction *ka,
 	regs->nip = (unsigned long) ka->sa.sa_handler;
 	/* enter the signal handler in big-endian mode */
 	regs->msr &= ~MSR_LE;
-	regs->trap = 0;
 	return 1;
 
 badframe:
@@ -1228,7 +1228,6 @@ int handle_signal32(unsigned long sig, struct k_sigaction *ka,
 	regs->nip = (unsigned long) ka->sa.sa_handler;
 	/* enter the signal handler in big-endian mode */
 	regs->msr &= ~MSR_LE;
-	regs->trap = 0;
 
 	return 1;
 

arch/powerpc/kernel/signal_64.c

@@ -178,7 +178,7 @@ static long restore_sigcontext(struct pt_regs *regs, sigset_t *set, int sig,
 	err |= __get_user(regs->xer, &sc->gp_regs[PT_XER]);
 	err |= __get_user(regs->ccr, &sc->gp_regs[PT_CCR]);
 	/* skip SOFTE */
-	err |= __get_user(regs->trap, &sc->gp_regs[PT_TRAP]);
+	regs->trap = 0;
 	err |= __get_user(regs->dar, &sc->gp_regs[PT_DAR]);
 	err |= __get_user(regs->dsisr, &sc->gp_regs[PT_DSISR]);
 	err |= __get_user(regs->result, &sc->gp_regs[PT_RESULT]);