m68k: add TIF_NOTIFY_RESUME and handle it.

TIF_NOTIFY_RESUME added (as bit 5).  That way nommu glue needs no changes at
all; mmu one needs just to replace jmi do_signal_return to jne do_signal_return
There we have flags shifted up, until bit 6 (SIGPENDING) is in MSBit; instead
of checking that MSBit is set (jmi) we check that MSBit or something below it
is set (jne); bits 0..4 are never set, so that's precisely "bit 6 or bit 5 is
set".

Usual handling of NOTIFY_RESUME/SIGPENDING is done in do_notify_resume(); glue
calls it instead of do_signal().
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/m68k/include/asm/thread_info.h

@@ -71,6 +71,7 @@ static inline struct thread_info *current_thread_info(void)
  * bits 0-7 are tested at every exception exit
  * bits 8-15 are also tested at syscall exit
  */
+#define TIF_NOTIFY_RESUME	5	/* callback before returning to user */
 #define TIF_SIGPENDING		6	/* signal pending */
 #define TIF_NEED_RESCHED	7	/* rescheduling necessary */
 #define TIF_DELAYED_TRACE	14	/* single step a syscall */

arch/m68k/kernel/entry_mm.S

@@ -148,7 +148,7 @@ syscall_exit_work:
 	jcs	do_trace_exit
 	jmi	do_delayed_trace
 	lslw	#8,%d0
-	jmi	do_signal_return
+	jne	do_signal_return
 	pea	resume_userspace
 	jra	schedule
 
@@ -172,7 +172,7 @@ exit_work:
 	| save top of frame
 	movel	%sp,%curptr@(TASK_THREAD+THREAD_ESP0)
 	lslb	#1,%d0
-	jmi	do_signal_return
+	jne	do_signal_return
 	pea	resume_userspace
 	jra	schedule
 
@@ -182,7 +182,7 @@ do_signal_return:
 	subql	#4,%sp			| dummy return address
 	SAVE_SWITCH_STACK
 	pea	%sp@(SWITCH_STACK_SIZE)
-	bsrl	do_signal
+	bsrl	do_notify_resume
 	addql	#4,%sp
 	RESTORE_SWITCH_STACK
 	addql	#4,%sp

arch/m68k/kernel/signal.c

@@ -43,6 +43,7 @@
 #include <linux/tty.h>
 #include <linux/binfmts.h>
 #include <linux/module.h>
+#include <linux/tracehook.h>
 
 #include <asm/setup.h>
 #include <asm/uaccess.h>
@@ -1154,7 +1155,7 @@ handle_signal(int sig, struct k_sigaction *ka, siginfo_t *info,
  * want to handle. Thus you cannot kill init even with a SIGKILL even by
  * mistake.
  */
-asmlinkage void do_signal(struct pt_regs *regs)
+static void do_signal(struct pt_regs *regs)
 {
 	siginfo_t info;
 	struct k_sigaction ka;
@@ -1186,3 +1187,15 @@ asmlinkage void do_signal(struct pt_regs *regs)
 		sigprocmask(SIG_SETMASK, &current->saved_sigmask, NULL);
 	}
 }
+
+void do_notify_resume(struct pt_regs *regs)
+{
+	if (test_thread_flag(TIF_SIGPENDING))
+		do_signal(regs);
+
+	if (test_and_clear_thread_flag(TIF_NOTIFY_RESUME)) {
+		tracehook_notify_resume(regs);
+		if (current->replacement_session_keyring)
+			key_replace_session_keyring();
+	}
+}

arch/m68k/platform/68328/entry.S

@@ -119,7 +119,7 @@ Lsignal_return:
 	subql	#4,%sp			/* dummy return address*/
 	SAVE_SWITCH_STACK
 	pea	%sp@(SWITCH_STACK_SIZE)
-	bsrw	do_signal
+	bsrw	do_notify_resume
 	addql	#4,%sp
 	RESTORE_SWITCH_STACK
 	addql	#4,%sp

arch/m68k/platform/68360/entry.S

@@ -115,7 +115,7 @@ Lsignal_return:
 	subql	#4,%sp			/* dummy return address*/
 	SAVE_SWITCH_STACK
 	pea	%sp@(SWITCH_STACK_SIZE)
-	bsrw	do_signal
+	bsrw	do_notify_resume
 	addql	#4,%sp
 	RESTORE_SWITCH_STACK
 	addql	#4,%sp

arch/m68k/platform/coldfire/entry.S

@@ -152,7 +152,7 @@ Lsignal_return:
 	subql	#4,%sp			/* dummy return address */
 	SAVE_SWITCH_STACK
 	pea	%sp@(SWITCH_STACK_SIZE)
-	jsr	do_signal
+	jsr	do_notify_resume
 	addql	#4,%sp
 	RESTORE_SWITCH_STACK
 	addql	#4,%sp