[PATCH 09/13] task_work: Decouple TIF_NOTIFY_SIGNAL and task_work

Eric W. Biederman
2022-03-09T16:50:30Z

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.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
fs/io-wq.c | 4 +++-
fs/io_uring.c | 4 +++-
include/linux/tracehook.h | 15 ++-------------
kernel/entry/kvm.c | 7 +++++--
4 files changed, 13 insertions(+), 17 deletions(-)

diff --git a/fs/io-wq.c b/fs/io-wq.c
index bb7f161bb19c..8b9147873c2c 100644
--- a/fs/io-wq.c
+++ b/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;
diff --git a/fs/io_uring.c b/fs/io_uring.c
index e85261079a78..d5fbae1030f9 100644
--- a/fs/io_uring.c
+++ b/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;
}

diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
index b44a7820c468..e5d676e841e3 100644
--- a/include/linux/tracehook.h
+++ b/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)
{
diff --git a/kernel/entry/kvm.c b/kernel/entry/kvm.c
index cabf36a489e4..3ab5f98988c3 100644
--- a/kernel/entry/kvm.c
+++ b/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);
--
2.29.2