[10/34] [S390] ptrace: fix return value of do_syscall_trace_enter()

[Greg KH <gregkh@suse.de>]

2.6.34-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Gerald Schaefer <gerald.schaefer@de.ibm.com>

commit 545c174d1f093a462b4bb9131b23d5ea72a600e1 upstream.

strace may change the system call number, so regs->gprs[2] must not
be read before tracehook_report_syscall_entry(). This fixes a bug
where "strace -f" will hang after a vfork().

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 arch/s390/kernel/ptrace.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- a/arch/s390/kernel/ptrace.c
+++ b/arch/s390/kernel/ptrace.c
@@ -632,7 +632,7 @@ long compat_arch_ptrace(struct task_stru
 
 asmlinkage long do_syscall_trace_enter(struct pt_regs *regs)
 {
-	long ret;
+	long ret = 0;
 
 	/* Do the secure computing check first. */
 	secure_computing(regs->gprs[2]);
@@ -641,7 +641,6 @@ asmlinkage long do_syscall_trace_enter(s
 	 * The sysc_tracesys code in entry.S stored the system
 	 * call number to gprs[2].
 	 */
-	ret = regs->gprs[2];
 	if (test_thread_flag(TIF_SYSCALL_TRACE) &&
 	    (tracehook_report_syscall_entry(regs) ||
 	     regs->gprs[2] >= NR_syscalls)) {
@@ -663,7 +662,7 @@ asmlinkage long do_syscall_trace_enter(s
 				    regs->gprs[2], regs->orig_gpr2,
 				    regs->gprs[3], regs->gprs[4],
 				    regs->gprs[5]);
-	return ret;
+	return ret ?: regs->gprs[2];
 }
 
 asmlinkage void do_syscall_trace_exit(struct pt_regs *regs)