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From:   Christoph Hellwig <hch@lst.de>
To:     axboe@kernel.dk
Cc:     linux-kernel@vger.kernel.org
Subject: [PATCH] task_work: simplify the task_work_add() interface
Date:   Wed, 23 Feb 2022 08:27:54 +0100
Message-Id: <20220223072754.616027-1-hch@lst.de>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Provide a low-level task_work_add_nonotify interface that just adds
the work to the list and open code the TWA_SIGNAL and TWA_NONE callers
using it.  task_work_add() itself now only handles the common TWA_RESUME
case and can drop the notify argument.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 arch/x86/kernel/cpu/mce/core.c |  2 +-
 arch/x86/mm/tlb.c              |  2 +-
 drivers/acpi/apei/ghes.c       |  3 +-
 drivers/android/binder.c       |  2 +-
 fs/file_table.c                |  2 +-
 fs/io-wq.c                     |  3 +-
 fs/io_uring.c                  | 16 +++++-----
 fs/namespace.c                 |  2 +-
 include/linux/task_work.h      | 11 ++-----
 include/linux/tracehook.h      |  2 +-
 kernel/events/uprobes.c        |  2 +-
 kernel/irq/manage.c            |  2 +-
 kernel/sched/fair.c            |  2 +-
 kernel/task_work.c             | 56 ++++++++++++++++++----------------
 kernel/time/posix-cpu-timers.c |  2 +-
 security/keys/keyctl.c         |  2 +-
 security/yama/yama_lsm.c       |  2 +-
 17 files changed, 55 insertions(+), 58 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index 5818b837fd4d4..a9da9a968163c 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -1349,7 +1349,7 @@ static void queue_task_work(struct mce *m, char *msg, void (*func)(struct callba
 	if (count > 1)
 		return;
 
-	task_work_add(current, &current->mce_kill_me, TWA_RESUME);
+	task_work_add(current, &current->mce_kill_me);
 }
 
 /* Handle unconfigured int18 (should never happen) */
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index a6cf56a149393..8db8f4f7001f8 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -355,7 +355,7 @@ static void l1d_flush_evaluate(unsigned long prev_mm, unsigned long next_mm,
 	if (this_cpu_read(cpu_info.smt_active)) {
 		clear_ti_thread_flag(&next->thread_info, TIF_SPEC_L1D_FLUSH);
 		next->l1d_flush_kill.func = l1d_flush_force_sigbus;
-		task_work_add(next, &next->l1d_flush_kill, TWA_RESUME);
+		task_work_add(next, &next->l1d_flush_kill);
 	}
 }
 
diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
index 0c5c9acc6254e..12bd63b9af308 100644
--- a/drivers/acpi/apei/ghes.c
+++ b/drivers/acpi/apei/ghes.c
@@ -988,8 +988,7 @@ static void ghes_proc_in_irq(struct irq_work *irq_work)
 		if (task_work_pending && current->mm != &init_mm) {
 			estatus_node->task_work.func = ghes_kick_task_work;
 			estatus_node->task_work_cpu = smp_processor_id();
-			ret = task_work_add(current, &estatus_node->task_work,
-					    TWA_RESUME);
+			ret = task_work_add(current, &estatus_node->task_work);
 			if (ret)
 				estatus_node->task_work.func = NULL;
 		}
diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 8351c5638880b..eeef8dfde606b 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -1858,7 +1858,7 @@ static void binder_deferred_fd_close(int fd)
 	close_fd_get_file(fd, &twcb->file);
 	if (twcb->file) {
 		filp_close(twcb->file, current->files);
-		task_work_add(current, &twcb->twork, TWA_RESUME);
+		task_work_add(current, &twcb->twork);
 	} else {
 		kfree(twcb);
 	}
diff --git a/fs/file_table.c b/fs/file_table.c
index 7d2e692b66a94..3c329359c18f8 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -375,7 +375,7 @@ void fput_many(struct file *file, unsigned int refs)
 
 		if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
 			init_task_work(&file->f_u.fu_rcuhead, ____fput);
-			if (!task_work_add(task, &file->f_u.fu_rcuhead, TWA_RESUME))
+			if (!task_work_add(task, &file->f_u.fu_rcuhead))
 				return;
 			/*
 			 * After this task has run exit_task_work(),
diff --git a/fs/io-wq.c b/fs/io-wq.c
index bb7f161bb19cd..23d628b591a7b 100644
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -362,7 +362,8 @@ static bool io_queue_worker_create(struct io_worker *worker,
 	atomic_inc(&wq->worker_refs);
 	init_task_work(&worker->create_work, func);
 	worker->create_index = acct->index;
-	if (!task_work_add(wq->task, &worker->create_work, TWA_SIGNAL)) {
+	if (!task_work_add_nonotify(wq->task, &worker->create_work)) {
+		set_notify_signal(wq->task);
 		/*
 		 * EXIT may have been set after checking it above, check after
 		 * adding the task_work and remove any creation item if it is
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 77b9c7e4793bf..94116a102dc61 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2374,7 +2374,6 @@ static void io_req_task_work_add(struct io_kiocb *req, bool priority)
 {
 	struct task_struct *tsk = req->task;
 	struct io_uring_task *tctx = tsk->io_uring;
-	enum task_work_notify_mode notify;
 	struct io_wq_work_node *node;
 	unsigned long flags;
 	bool running;
@@ -2397,14 +2396,15 @@ static void io_req_task_work_add(struct io_kiocb *req, bool priority)
 
 	/*
 	 * SQPOLL kernel thread doesn't need notification, just a wakeup. For
-	 * all other cases, use TWA_SIGNAL unconditionally to ensure we're
-	 * processing task_work. There's no reliable way to tell if TWA_RESUME
-	 * will do the job.
+	 * all other cases, use set_notify_signal unconditionally to ensure
+	 * we're processing the task_work. There's no reliable way to tell if
+	 * task_work_add will do the job.
 	 */
-	notify = (req->ctx->flags & IORING_SETUP_SQPOLL) ? TWA_NONE : TWA_SIGNAL;
-	if (likely(!task_work_add(tsk, &tctx->task_work, notify))) {
-		if (notify == TWA_NONE)
+	if (likely(!task_work_add_nonotify(tsk, &tctx->task_work))) {
+		if (req->ctx->flags & IORING_SETUP_SQPOLL)
 			wake_up_process(tsk);
+		else
+			set_notify_signal(tsk);
 		return;
 	}
 
@@ -9606,7 +9606,7 @@ static __cold void io_ring_exit_work(struct work_struct *work)
 					ctx_node);
 		/* don't spin on a single task if cancellation failed */
 		list_rotate_left(&ctx->tctx_list);
-		ret = task_work_add(node->task, &exit.task_work, TWA_SIGNAL);
+		ret = task_work_add_nonotify(node->task, &exit.task_work);
 		if (WARN_ON_ONCE(ret))
 			continue;
 
diff --git a/fs/namespace.c b/fs/namespace.c
index de6fae84f1a1a..a482b41621866 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1249,7 +1249,7 @@ static void mntput_no_expire(struct mount *mnt)
 		struct task_struct *task = current;
 		if (likely(!(task->flags & PF_KTHREAD))) {
 			init_task_work(&mnt->mnt_rcu, __cleanup_mnt);
-			if (!task_work_add(task, &mnt->mnt_rcu, TWA_RESUME))
+			if (!task_work_add(task, &mnt->mnt_rcu))
 				return;
 		}
 		if (llist_add(&mnt->mnt_llist, &delayed_mntput_list))
diff --git a/include/linux/task_work.h b/include/linux/task_work.h
index 5b8a93f288bb4..af27deee1a559 100644
--- a/include/linux/task_work.h
+++ b/include/linux/task_work.h
@@ -13,14 +13,9 @@ init_task_work(struct callback_head *twork, task_work_func_t func)
 	twork->func = func;
 }
 
-enum task_work_notify_mode {
-	TWA_NONE,
-	TWA_RESUME,
-	TWA_SIGNAL,
-};
-
-int task_work_add(struct task_struct *task, struct callback_head *twork,
-			enum task_work_notify_mode mode);
+int task_work_add(struct task_struct *task, struct callback_head *twork);
+int task_work_add_nonotify(struct task_struct *task,
+		struct callback_head *twork);
 
 struct callback_head *task_work_cancel_match(struct task_struct *task,
 	bool (*match)(struct callback_head *, void *data), void *data);
diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index 88c007ab5ebc7..910fd2d6467e7 100644
--- a/include/linux/tracehook.h
+++ b/include/linux/tracehook.h
@@ -202,7 +202,7 @@ static inline void tracehook_notify_resume(struct pt_regs *regs)
 
 /*
  * 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
+ * is currently used by 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)
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 6357c3580d07b..6c12d9f0dc647 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1823,7 +1823,7 @@ void uprobe_copy_process(struct task_struct *t, unsigned long flags)
 
 	t->utask->dup_xol_addr = area->vaddr;
 	init_task_work(&t->utask->dup_xol_work, dup_xol_work);
-	task_work_add(t, &t->utask->dup_xol_work, TWA_RESUME);
+	task_work_add(t, &t->utask->dup_xol_work);
 }
 
 /*
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index f23ffd30385b1..4557319303374 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -1268,7 +1268,7 @@ static int irq_thread(void *data)
 		handler_fn = irq_thread_fn;
 
 	init_task_work(&on_exit_work, irq_thread_dtor);
-	task_work_add(current, &on_exit_work, TWA_NONE);
+	task_work_add_nonotify(current, &on_exit_work);
 
 	irq_thread_check_affinity(desc, action);
 
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5146163bfabb9..616626719c5f5 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2880,7 +2880,7 @@ static void task_tick_numa(struct rq *rq, struct task_struct *curr)
 		curr->node_stamp += period;
 
 		if (!time_before(jiffies, curr->mm->numa_next_scan))
-			task_work_add(curr, work, TWA_RESUME);
+			task_work_add(curr, work);
 	}
 }
 
diff --git a/kernel/task_work.c b/kernel/task_work.c
index 1698fbe6f0e13..4a547d80d6493 100644
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -6,22 +6,16 @@
 static struct callback_head work_exited; /* all we need is ->next == NULL */
 
 /**
- * task_work_add - ask the @task to execute @work->func()
+ * task_work_add_nonotify - ask the @task to execute @work->func()
  * @task: the task which should run the callback
  * @work: the callback to run
  * @notify: how to notify the targeted task
  *
- * Queue @work for task_work_run() below and notify the @task if @notify
- * is @TWA_RESUME or @TWA_SIGNAL. @TWA_SIGNAL works like signals, in that the
- * it will interrupt the targeted task and run the task_work. @TWA_RESUME
- * work is run only when the task exits the kernel and returns to user mode,
- * or before entering guest mode. Fails if the @task is exiting/exited and thus
- * it can't process this @work. Otherwise @work->func() will be called when the
- * @task goes through one of the aforementioned transitions, or exits.
+ * Queue @work for task_work_run() below.  If the targeted task is exiting, then
+ * an error is returned and the work item is not queued. It's up to the caller
+ * to arrange for an alternative mechanism in that case.
  *
- * If the targeted task is exiting, then an error is returned and the work item
- * is not queued. It's up to the caller to arrange for an alternative mechanism
- * in that case.
+ * The caller needs to notify @task to make sure @work is actually run.
  *
  * Note: there is no ordering guarantee on works queued here. The task_work
  * list is LIFO.
@@ -29,8 +23,7 @@ static struct callback_head work_exited; /* all we need is ->next == NULL */
  * RETURNS:
  * 0 if succeeds or -ESRCH.
  */
-int task_work_add(struct task_struct *task, struct callback_head *work,
-		  enum task_work_notify_mode notify)
+int task_work_add_nonotify(struct task_struct *task, struct callback_head *work)
 {
 	struct callback_head *head;
 
@@ -44,23 +37,32 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
 		work->next = head;
 	} while (cmpxchg(&task->task_works, head, work) != head);
 
-	switch (notify) {
-	case TWA_NONE:
-		break;
-	case TWA_RESUME:
-		set_notify_resume(task);
-		break;
-	case TWA_SIGNAL:
-		set_notify_signal(task);
-		break;
-	default:
-		WARN_ON_ONCE(1);
-		break;
-	}
-
 	return 0;
 }
 
+/**
+ * task_work_add - ask the @task to execute @work->func()
+ * @task: the task which should run the callback
+ * @work: the callback to run
+ * @notify: how to notify the targeted task
+ *
+ * Queue @work using task_work_add_nonotify() and notify the task to actually
+ * run it when the task exits the kernel and returns to user mode, or before
+ * entering guest mode.
+ *
+ * RETURNS:
+ * 0 if succeeds or -ESRCH.
+ */
+int task_work_add(struct task_struct *task, struct callback_head *work)
+{
+	int ret;
+
+	ret = task_work_add_nonotify(task, work);
+	if (!ret)
+		set_notify_resume(task);
+	return ret;
+}
+
 /**
  * task_work_cancel_match - cancel a pending work added by task_work_add()
  * @task: the task which should execute the work
diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 96b4e78104266..c8808b32dc144 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -1201,7 +1201,7 @@ static inline void __run_posix_cpu_timers(struct task_struct *tsk)
 
 	/* Schedule task work to actually expire the timers */
 	tsk->posix_cputimers_work.scheduled = true;
-	task_work_add(tsk, &tsk->posix_cputimers_work.work, TWA_RESUME);
+	task_work_add(tsk, &tsk->posix_cputimers_work.work);
 }
 
 static inline bool posix_cpu_timers_enable_work(struct task_struct *tsk,
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 96a92a645216d..331a825ff6616 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -1693,7 +1693,7 @@ long keyctl_session_to_parent(void)
 
 	/* the replacement session keyring is applied just prior to userspace
 	 * restarting */
-	ret = task_work_add(parent, newwork, TWA_RESUME);
+	ret = task_work_add(parent, newwork);
 	if (!ret)
 		newwork = NULL;
 unlock:
diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
index 06e226166aab3..2af248939dd46 100644
--- a/security/yama/yama_lsm.c
+++ b/security/yama/yama_lsm.c
@@ -99,7 +99,7 @@ static void report_access(const char *access, struct task_struct *target,
 	info->access = access;
 	info->target = target;
 	info->agent = agent;
-	if (task_work_add(current, &info->work, TWA_RESUME) == 0)
+	if (task_work_add(current, &info->work) == 0)
 		return; /* success */
 
 	WARN(1, "report_access called from exiting task");
-- 
2.30.2