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>

3 files changed, 4 insertions, 3 deletions

diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c
index 7109f5b1baa8..2300426e531a 100644
--- a/arch/powerpc/kernel/signal.c
+++ b/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,
diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
index 266610119f66..b96a3a010c26 100644
--- a/arch/powerpc/kernel/signal_32.c
+++ b/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;
 
diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 2fe6fc64b614..27c4a4584f80 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/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]);