task_work: Decouple TIF_NOTIFY_SIGNAL and task_work

There are a small handful of reasons besides pending signals that the
kernel might want to break out of interruptible sleeps.  The flag
TIF_NOTIFY_SIGNAL and the helpers that set and clear TIF_NOTIFY_SIGNAL
provide that the infrastructure for breaking out of interruptible
sleeps and entering the return to user space slow path for those
cases.

Expand tracehook_notify_signal inline in it's callers and remove it,
which makes clear that TIF_NOTIFY_SIGNAL and task_work are separate
concepts.

Update the comment on set_notify_signal to more accurately describe
it's purpose.

Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20220309162454.123006-9-ebiederm@xmission.com
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

fs/io-wq.c

@@ -515,7 +515,9 @@ static bool io_flush_signals(void)
 {
 	if (unlikely(test_thread_flag(TIF_NOTIFY_SIGNAL))) {
 		__set_current_state(TASK_RUNNING);
-		tracehook_notify_signal();
+		clear_notify_signal();
+		if (task_work_pending(current))
+			task_work_run();
 		return true;
 	}
 	return false;

fs/io_uring.c

@@ -2592,7 +2592,9 @@ static inline bool io_run_task_work(void)
 {
 	if (test_thread_flag(TIF_NOTIFY_SIGNAL) || task_work_pending(current)) {
 		__set_current_state(TASK_RUNNING);
-		tracehook_notify_signal();
+		clear_notify_signal();
+		if (task_work_pending(current))
+			task_work_run();
 		return true;
 	}
 

include/linux/tracehook.h

@@ -113,19 +113,8 @@ static inline void clear_notify_signal(void)
 }
 
 /*
- * called by exit_to_user_mode_loop() if ti_work & _TIF_NOTIFY_SIGNAL. This
- * is currently used by TWA_SIGNAL based task_work, which requires breaking
- * wait loops to ensure that task_work is noticed and run.
- */
-static inline void tracehook_notify_signal(void)
-{
-	clear_notify_signal();
-	if (task_work_pending(current))
-		task_work_run();
-}
-
-/*
- * Called when we have work to process from exit_to_user_mode_loop()
+ * Called to break out of interruptible wait loops, and enter the
+ * exit_to_user_mode_loop().
  */
 static inline void set_notify_signal(struct task_struct *task)
 {

kernel/entry/kvm.c

@@ -8,8 +8,11 @@ static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work)
 	do {
 		int ret;
 
-		if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
-			tracehook_notify_signal();
+		if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL)) {
+			clear_notify_signal();
+			if (task_work_pending(current))
+				task_work_run();
+		}
 
 		if (ti_work & _TIF_SIGPENDING) {
 			kvm_handle_signal_exit(vcpu);