task_work: Introduce task_work_pending

Wrap the test of task->task_works in a helper function to make
it clear what is being tested.

All of the other readers of task->task_work use READ_ONCE and this is
even necessary on current as other processes can update
task->task_work.  So for consistency I have added READ_ONCE into
task_work_pending.

Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20220309162454.123006-7-ebiederm@xmission.com
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

fs/io_uring.c

@@ -2590,7 +2590,7 @@ static inline unsigned int io_sqring_entries(struct io_ring_ctx *ctx)
 
 static inline bool io_run_task_work(void)
 {
-	if (test_thread_flag(TIF_NOTIFY_SIGNAL) || current->task_works) {
+	if (test_thread_flag(TIF_NOTIFY_SIGNAL) || task_work_pending(current)) {
 		__set_current_state(TASK_RUNNING);
 		tracehook_notify_signal();
 		return true;
@@ -7602,7 +7602,7 @@ static int io_sq_thread(void *data)
 		}
 
 		prepare_to_wait(&sqd->wait, &wait, TASK_INTERRUPTIBLE);
-		if (!io_sqd_events_pending(sqd) && !current->task_works) {
+		if (!io_sqd_events_pending(sqd) && !task_work_pending(current)) {
 			bool needs_sched = true;
 
 			list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) {
@@ -10321,7 +10321,7 @@ static __cold void __io_uring_show_fdinfo(struct io_ring_ctx *ctx,
 
 		hlist_for_each_entry(req, list, hash_node)
 			seq_printf(m, "  op=%d, task_works=%d\n", req->opcode,
-					req->task->task_works != NULL);
+					task_work_pending(req->task));
 	}
 
 	seq_puts(m, "CqOverflowList:\n");

include/linux/task_work.h

@@ -19,6 +19,11 @@ enum task_work_notify_mode {
 	TWA_SIGNAL,
 };
 
+static inline bool task_work_pending(struct task_struct *task)
+{
+	return READ_ONCE(task->task_works);
+}
+
 int task_work_add(struct task_struct *task, struct callback_head *twork,
 			enum task_work_notify_mode mode);
 

include/linux/tracehook.h

@@ -90,7 +90,7 @@ static inline void tracehook_notify_resume(struct pt_regs *regs)
 	 * hlist_add_head(task->task_works);
 	 */
 	smp_mb__after_atomic();
-	if (unlikely(current->task_works))
+	if (unlikely(task_work_pending(current)))
 		task_work_run();
 
 #ifdef CONFIG_KEYS_REQUEST_CACHE
@@ -115,7 +115,7 @@ static inline void tracehook_notify_signal(void)
 {
 	clear_thread_flag(TIF_NOTIFY_SIGNAL);
 	smp_mb__after_atomic();
-	if (current->task_works)
+	if (task_work_pending(current))
 		task_work_run();
 }
 

kernel/signal.c

@@ -2344,7 +2344,7 @@ static void ptrace_do_notify(int signr, int exit_code, int why)
 void ptrace_notify(int exit_code)
 {
 	BUG_ON((exit_code & (0x7f | ~0xffff)) != SIGTRAP);
-	if (unlikely(current->task_works))
+	if (unlikely(task_work_pending(current)))
 		task_work_run();
 
 	spin_lock_irq(&current->sighand->siglock);
@@ -2626,7 +2626,7 @@ bool get_signal(struct ksignal *ksig)
 	struct signal_struct *signal = current->signal;
 	int signr;
 
-	if (unlikely(current->task_works))
+	if (unlikely(task_work_pending(current)))
 		task_work_run();
 
 	/*

kernel/task_work.c

@@ -78,7 +78,7 @@ task_work_cancel_match(struct task_struct *task,
 	struct callback_head *work;
 	unsigned long flags;
 
-	if (likely(!task->task_works))
+	if (likely(!task_work_pending(task)))
 		return NULL;
 	/*
 	 * If cmpxchg() fails we continue without updating pprev.