[tip: timers/core] timerfd: Provide timerfd_resume()

[tip-bot2 for Thomas Gleixner]

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     66f7b0c8aadd2785fc29f2c71477ebc16f4e38cc
Gitweb:        https://git.kernel.org/tip/66f7b0c8aadd2785fc29f2c71477ebc16f4e38cc
Author:        Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate:    Tue, 13 Jul 2021 15:39:50 +02:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Tue, 10 Aug 2021 17:57:22 +02:00

timerfd: Provide timerfd_resume()

Resuming timekeeping is a clock-was-set event and uses the clock-was-set
notification mechanism. This is in the way of making the clock-was-set
update for hrtimers selective so unnecessary IPIs are avoided when a CPU
base does not have timers queued which are affected by the clock setting.

Provide a seperate timerfd_resume() interface so the resume logic and the
clock-was-set mechanism can be distangled in the core code.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210713135158.395287410@xxxxxxxxxxxxx

---
 fs/timerfd.c            | 16 ++++++++++++++++
 include/linux/hrtimer.h |  2 ++
 2 files changed, 18 insertions(+)

diff --git a/fs/timerfd.c b/fs/timerfd.c
index c5509d2..e9c96a0 100644
--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -115,6 +115,22 @@ void timerfd_clock_was_set(void)
 	rcu_read_unlock();
 }
 
+static void timerfd_resume_work(struct work_struct *work)
+{
+	timerfd_clock_was_set();
+}
+
+static DECLARE_WORK(timerfd_work, timerfd_resume_work);
+
+/*
+ * Invoked from timekeeping_resume(). Defer the actual update to work so
+ * timerfd_clock_was_set() runs in task context.
+ */
+void timerfd_resume(void)
+{
+	schedule_work(&timerfd_work);
+}
+
 static void __timerfd_remove_cancel(struct timerfd_ctx *ctx)
 {
 	if (ctx->might_cancel) {
diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 77295af..253c6e2 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -349,8 +349,10 @@ hrtimer_expires_remaining_adjusted(const struct hrtimer *timer)
 
 #ifdef CONFIG_TIMERFD
 extern void timerfd_clock_was_set(void);
+extern void timerfd_resume(void);
 #else
 static inline void timerfd_clock_was_set(void) { }
+static inline void timerfd_resume(void) { }
 #endif
 extern void hrtimers_resume(void);