1 files changed, 33 insertions, 25 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index 09019017d669..83fcbaf0e82d 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1718,9 +1718,8 @@ void force_sigsegv(int sig)
 		force_sig(SIGSEGV);
 }
 
-int force_sig_fault_to_task(int sig, int code, void __user *addr
-	___ARCH_SI_IA64(int imm, unsigned int flags, unsigned long isr)
-	, struct task_struct *t)
+int force_sig_fault_to_task(int sig, int code, void __user *addr,
+			    struct task_struct *t)
 {
 	struct kernel_siginfo info;
 
@@ -1729,24 +1728,15 @@ int force_sig_fault_to_task(int sig, int code, void __user *addr
 	info.si_errno = 0;
 	info.si_code  = code;
 	info.si_addr  = addr;
-#ifdef __ia64__
-	info.si_imm = imm;
-	info.si_flags = flags;
-	info.si_isr = isr;
-#endif
 	return force_sig_info_to_task(&info, t, HANDLER_CURRENT);
 }
 
-int force_sig_fault(int sig, int code, void __user *addr
-	___ARCH_SI_IA64(int imm, unsigned int flags, unsigned long isr))
+int force_sig_fault(int sig, int code, void __user *addr)
 {
-	return force_sig_fault_to_task(sig, code, addr
-				       ___ARCH_SI_IA64(imm, flags, isr), current);
+	return force_sig_fault_to_task(sig, code, addr, current);
 }
 
-int send_sig_fault(int sig, int code, void __user *addr
-	___ARCH_SI_IA64(int imm, unsigned int flags, unsigned long isr)
-	, struct task_struct *t)
+int send_sig_fault(int sig, int code, void __user *addr, struct task_struct *t)
 {
 	struct kernel_siginfo info;
 
@@ -1755,11 +1745,6 @@ int send_sig_fault(int sig, int code, void __user *addr
 	info.si_errno = 0;
 	info.si_code  = code;
 	info.si_addr  = addr;
-#ifdef __ia64__
-	info.si_imm = imm;
-	info.si_flags = flags;
-	info.si_isr = isr;
-#endif
 	return send_sig_info(info.si_signo, &info, t);
 }
 
@@ -2329,15 +2314,38 @@ static int ptrace_stop(int exit_code, int why, unsigned long message,
 		do_notify_parent_cldstop(current, false, why);
 
 	/*
-	 * Don't want to allow preemption here, because
-	 * sys_ptrace() needs this task to be inactive.
+	 * The previous do_notify_parent_cldstop() invocation woke ptracer.
+	 * One a PREEMPTION kernel this can result in preemption requirement
+	 * which will be fulfilled after read_unlock() and the ptracer will be
+	 * put on the CPU.
+	 * The ptracer is in wait_task_inactive(, __TASK_TRACED) waiting for
+	 * this task wait in schedule(). If this task gets preempted then it
+	 * remains enqueued on the runqueue. The ptracer will observe this and
+	 * then sleep for a delay of one HZ tick. In the meantime this task
+	 * gets scheduled, enters schedule() and will wait for the ptracer.
+	 *
+	 * This preemption point is not bad from a correctness point of
+	 * view but extends the runtime by one HZ tick time due to the
+	 * ptracer's sleep.  The preempt-disable section ensures that there
+	 * will be no preemption between unlock and schedule() and so
+	 * improving the performance since the ptracer will observe that
+	 * the tracee is scheduled out once it gets on the CPU.
 	 *
-	 * XXX: implement read_unlock_no_resched().
+	 * On PREEMPT_RT locking tasklist_lock does not disable preemption.
+	 * Therefore the task can be preempted after do_notify_parent_cldstop()
+	 * before unlocking tasklist_lock so there is no benefit in doing this.
+	 *
+	 * In fact disabling preemption is harmful on PREEMPT_RT because
+	 * the spinlock_t in cgroup_enter_frozen() must not be acquired
+	 * with preemption disabled due to the 'sleeping' spinlock
+	 * substitution of RT.
 	 */
-	preempt_disable();
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+		preempt_disable();
 	read_unlock(&tasklist_lock);
 	cgroup_enter_frozen();
-	preempt_enable_no_resched();
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
+		preempt_enable_no_resched();
 	schedule();
 	cgroup_leave_frozen(true);