[PATCH] Introduce TIF_IRET and use it to disable sysexit

This patch introduces a new flag called TIF_IRET and uses it in place
of TIF_SIGPENDING when that flag is used to force return via iret.

This avoids the overhead of calling do_signal and makes the code
easier to understand.

arch/i386/kernel/ioport.c

@@ -124,6 +124,6 @@ asmlinkage int sys_iopl(unsigned long unused)
 	}
 	regs->eflags = (regs->eflags & 0xffffcfff) | (level << 12);
 	/* Make sure we return the long way (not sysenter) */
-	set_thread_flag(TIF_SIGPENDING);
+	set_thread_flag(TIF_IRET);
 	return 0;
 }

arch/i386/kernel/process.c

@@ -555,7 +555,7 @@ asmlinkage int sys_execve(struct pt_regs regs)
 	if (error == 0) {
 		current->ptrace &= ~PT_DTRACE;
 		/* Make sure we don't return using sysenter.. */
-		set_thread_flag(TIF_SIGPENDING);
+		set_thread_flag(TIF_IRET);
 	}
 	putname(filename);
 out:

arch/i386/kernel/signal.c

@@ -617,4 +617,6 @@ void do_notify_resume(struct pt_regs *regs, sigset_t *oldset,
 	/* deal with pending signal delivery */
 	if (thread_info_flags & _TIF_SIGPENDING)
 		do_signal(regs,oldset);
+	
+	clear_thread_flag(TIF_IRET);
 }

include/asm-i386/thread_info.h

@@ -110,6 +110,7 @@ static inline struct thread_info *current_thread_info(void)
 #define TIF_SIGPENDING		2	/* signal pending */
 #define TIF_NEED_RESCHED	3	/* rescheduling necessary */
 #define TIF_SINGLESTEP		4	/* restore singlestep on return to user mode */
+#define TIF_IRET		5	/* return with iret */
 #define TIF_USEDFPU		16	/* FPU was used by this task this quantum (SMP) */
 #define TIF_POLLING_NRFLAG	17	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 
@@ -118,6 +119,7 @@ static inline struct thread_info *current_thread_info(void)
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
+#define _TIF_IRET		(1<<TIF_IRET)
 #define _TIF_USEDFPU		(1<<TIF_USEDFPU)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)