um: Re-evaluate thread flags repeatedly

The thread flags may change during their processing.
For example a task_work can queue a new signal to be sent.
This signal should be delivered before returning to usespace again.

Evaluate the flags repeatedly similar to other architectures.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Reviewed-by: Nam Cao <namcao@linutronix.de>
Link: https://patch.msgid.link/20250704-uml-thread_flags-v1-1-0e293fd8d627@linutronix.de
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Author: t-8ch

arch/um/include/asm/thread_info.h

@@ -52,7 +52,11 @@ struct thread_info {
 #define _TIF_NOTIFY_SIGNAL	(1 << TIF_NOTIFY_SIGNAL)
 #define _TIF_MEMDIE		(1 << TIF_MEMDIE)
 #define _TIF_SYSCALL_AUDIT	(1 << TIF_SYSCALL_AUDIT)
+#define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
 #define _TIF_SECCOMP		(1 << TIF_SECCOMP)
 #define _TIF_SINGLESTEP		(1 << TIF_SINGLESTEP)
 
+#define _TIF_WORK_MASK		(_TIF_NEED_RESCHED | _TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL | \
+				 _TIF_NOTIFY_RESUME)
+
 #endif

arch/um/kernel/process.c

@@ -82,14 +82,18 @@ struct task_struct *__switch_to(struct task_struct *from, struct task_struct *to
 void interrupt_end(void)
 {
 	struct pt_regs *regs = &current->thread.regs;
-
-	if (need_resched())
-		schedule();
-	if (test_thread_flag(TIF_SIGPENDING) ||
-	    test_thread_flag(TIF_NOTIFY_SIGNAL))
-		do_signal(regs);
-	if (test_thread_flag(TIF_NOTIFY_RESUME))
-		resume_user_mode_work(regs);
+	unsigned long thread_flags;
+
+	thread_flags = read_thread_flags();
+	while (thread_flags & _TIF_WORK_MASK) {
+		if (thread_flags & _TIF_NEED_RESCHED)
+			schedule();
+		if (thread_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
+			do_signal(regs);
+		if (thread_flags & _TIF_NOTIFY_RESUME)
+			resume_user_mode_work(regs);
+		thread_flags = read_thread_flags();
+	}
 }
 
 int get_current_pid(void)