If task_work has already been run on task exit, we don't always know
if it's safe to run again. Check for task_work_exited in the
task_work_pending() helper. This makes it less fragile in calling
from the exit files path, for example.
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
include/linux/task_work.h | 4 +++-
kernel/task_work.c | 8 ++++----
2 files changed, 7 insertions(+), 5 deletions(-)
diff --git a/include/linux/task_work.h b/include/linux/task_work.h
index 54c911bbf754..24f977a8fc35 100644
--- a/include/linux/task_work.h
+++ b/include/linux/task_work.h
@@ -7,6 +7,8 @@
typedef void (*task_work_func_t)(struct callback_head *);
+extern struct callback_head task_work_exited;
+
static inline void
init_task_work(struct callback_head *twork, task_work_func_t func)
{
@@ -19,7 +21,7 @@ void __task_work_run(void);
static inline bool task_work_pending(void)
{
- return current->task_works;
+ return current->task_works && current->task_works != &task_work_exited;
}
static inline void task_work_run(void)
diff --git a/kernel/task_work.c b/kernel/task_work.c
index 9620333423a3..d6a8b4ab4858 100644
--- a/kernel/task_work.c
+++ b/kernel/task_work.c
@@ -3,7 +3,7 @@
#include <linux/task_work.h>
#include <linux/tracehook.h>
-static struct callback_head work_exited; /* all we need is ->next == NULL */
+struct callback_head task_work_exited = { };
/**
* task_work_add - ask the @task to execute @work->func()
@@ -31,7 +31,7 @@ task_work_add(struct task_struct *task, struct callback_head *work, bool notify)
do {
head = READ_ONCE(task->task_works);
- if (unlikely(head == &work_exited))
+ if (unlikely(head == &task_work_exited))
return -ESRCH;
work->next = head;
} while (cmpxchg(&task->task_works, head, work) != head);
@@ -95,14 +95,14 @@ void __task_work_run(void)
for (;;) {
/*
* work->func() can do task_work_add(), do not set
- * work_exited unless the list is empty.
+ * task_work_exited unless the list is empty.
*/
do {
head = NULL;
work = READ_ONCE(task->task_works);
if (!work) {
if (task->flags & PF_EXITING)
- head = &work_exited;
+ head = &task_work_exited;
else
break;
}
--
2.26.0
