ptrace: x86: change syscall_trace_leave() to rely on tracehook when stepping

Suggested by Roland.

Unlike powepc, x86 always calls tracehook_report_syscall_exit(step) with
step = 0, and sends the trap by hand.

This results in unnecessary SIGTRAP when PTRACE_SINGLESTEP follows the
syscall-exit stop.

Change syscall_trace_leave() to pass the correct "step" argument to
tracehook and remove the send_sigtrap() logic.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Cc: <linux-arch@vger.kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 14 deletions

diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 77b60085a810..2779321046bd 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -1767,29 +1767,22 @@ asmregparm long syscall_trace_enter(struct pt_regs *regs)
 
 asmregparm void syscall_trace_leave(struct pt_regs *regs)
 {
+        bool step;
+
         if (unlikely(current->audit_context))
                 audit_syscall_exit(AUDITSC_RESULT(regs->ax), regs->ax);
 
         if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
                 trace_sys_exit(regs, regs->ax);
 
-        if (test_thread_flag(TIF_SYSCALL_TRACE))
-                tracehook_report_syscall_exit(regs, 0);
-
         /*
          * If TIF_SYSCALL_EMU is set, we only get here because of
          * TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
          * We already reported this syscall instruction in
-         * syscall_trace_enter(), so don't do any more now.
-         */
-        if (unlikely(test_thread_flag(TIF_SYSCALL_EMU)))
-                return;
-
-        /*
-         * If we are single-stepping, synthesize a trap to follow the
-         * system call instruction.
+         * syscall_trace_enter().
          */
-        if (test_thread_flag(TIF_SINGLESTEP) &&
-            tracehook_consider_fatal_signal(current, SIGTRAP))
-                send_sigtrap(current, regs, 0, TRAP_BRKPT);
+        step = unlikely(test_thread_flag(TIF_SINGLESTEP)) &&
+                        !test_thread_flag(TIF_SYSCALL_EMU);
+        if (step || test_thread_flag(TIF_SYSCALL_TRACE))
+                tracehook_report_syscall_exit(regs, step);
 }