Revert "signal, x86: Delay calling signals in atomic on RT enabled kernels"

Revert commit bf9ad37dc8. It needs to be better encapsulated and
generalized.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

arch/x86/Kconfig

@@ -122,7 +122,6 @@ config X86
 	select ARCH_WANT_GENERAL_HUGETLB
 	select ARCH_WANT_HUGE_PMD_SHARE
 	select ARCH_WANT_LD_ORPHAN_WARN
-	select ARCH_WANTS_RT_DELAYED_SIGNALS
 	select ARCH_WANTS_THP_SWAP		if X86_64
 	select ARCH_HAS_PARANOID_L1D_FLUSH
 	select BUILDTIME_TABLE_SORT

include/linux/sched.h

@@ -1090,9 +1090,6 @@ struct task_struct {
 	/* Restored if set_restore_sigmask() was used: */
 	sigset_t			saved_sigmask;
 	struct sigpending		pending;
-#ifdef CONFIG_RT_DELAYED_SIGNALS
-	struct kernel_siginfo		forced_info;
-#endif
 	unsigned long			sas_ss_sp;
 	size_t				sas_ss_size;
 	unsigned int			sas_ss_flags;

kernel/Kconfig.preempt

@@ -133,14 +133,4 @@ config SCHED_CORE
 	  which is the likely usage by Linux distributions, there should
 	  be no measurable impact on performance.
 
-config ARCH_WANTS_RT_DELAYED_SIGNALS
-	bool
-	help
-	  This option is selected by architectures where raising signals
-	  can happen in atomic contexts on PREEMPT_RT enabled kernels. This
-	  option delays raising the signal until the return to user space
-	  loop where it is also delivered. X86 requires this to deliver
-	  signals from trap handlers which run on IST stacks.
 
-config RT_DELAYED_SIGNALS
-	def_bool PREEMPT_RT && ARCH_WANTS_RT_DELAYED_SIGNALS

kernel/entry/common.c

@@ -142,18 +142,6 @@ void noinstr exit_to_user_mode(void)
 /* Workaround to allow gradual conversion of architecture code */
 void __weak arch_do_signal_or_restart(struct pt_regs *regs) { }
 
-#ifdef CONFIG_RT_DELAYED_SIGNALS
-static inline void raise_delayed_signal(void)
-{
-	if (unlikely(current->forced_info.si_signo)) {
-		force_sig_info(&current->forced_info);
-		current->forced_info.si_signo = 0;
-	}
-}
-#else
-static inline void raise_delayed_signal(void) { }
-#endif
-
 static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
 					    unsigned long ti_work)
 {
@@ -168,8 +156,6 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
 		if (ti_work & _TIF_NEED_RESCHED)
 			schedule();
 
-		raise_delayed_signal();
-
 		if (ti_work & _TIF_UPROBE)
 			uprobe_notify_resume(regs);
 

kernel/signal.c

@@ -1307,43 +1307,6 @@ enum sig_handler {
 	HANDLER_EXIT,	 /* Only visible as the process exit code */
 };
 
-/*
- * On some archictectures, PREEMPT_RT has to delay sending a signal from a
- * trap since it cannot enable preemption, and the signal code's
- * spin_locks turn into mutexes. Instead, it must set TIF_NOTIFY_RESUME
- * which will send the signal on exit of the trap.
- */
-#ifdef CONFIG_RT_DELAYED_SIGNALS
-static inline bool force_sig_delayed(struct kernel_siginfo *info,
-				     struct task_struct *t)
-{
-	if (!in_atomic())
-		return false;
-
-	if (WARN_ON_ONCE(t->forced_info.si_signo))
-		return true;
-
-	if (is_si_special(info)) {
-		WARN_ON_ONCE(info != SEND_SIG_PRIV);
-		t->forced_info.si_signo = info->si_signo;
-		t->forced_info.si_errno = 0;
-		t->forced_info.si_code = SI_KERNEL;
-		t->forced_info.si_pid = 0;
-		t->forced_info.si_uid = 0;
-	} else {
-		t->forced_info = *info;
-	}
-	set_tsk_thread_flag(t, TIF_NOTIFY_RESUME);
-	return true;
-}
-#else
-static inline bool force_sig_delayed(struct kernel_siginfo *info,
-				     struct task_struct *t)
-{
-	return false;
-}
-#endif
-
 /*
  * Force a signal that the process can't ignore: if necessary
  * we unblock the signal and change any SIG_IGN to SIG_DFL.
@@ -1364,9 +1327,6 @@ force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t,
 	struct k_sigaction *action;
 	int sig = info->si_signo;
 
-	if (force_sig_delayed(info, t))
-		return 0;
-
 	spin_lock_irqsave(&t->sighand->siglock, flags);
 	action = &t->sighand->action[sig-1];
 	ignored = action->sa.sa_handler == SIG_IGN;