sched/mmcid: Switch over to the new mechanism

Now that all pieces are in place, change the implementations of
sched_mm_cid_fork() and sched_mm_cid_exit() to adhere to the new strict
ownership scheme and switch context_switch() over to use the new
mm_cid_schedin() functionality.

The common case is that there is no mode change required, which makes
fork() and exit() just update the user count and the constraints.

In case that a new user would exceed the CID space limit the fork() context
handles the transition to per CPU mode with mm::mm_cid::mutex held. exit()
handles the transition back to per task mode when the user count drops
below the switch back threshold. fork() might also be forced to handle a
deferred switch back to per task mode, when a affinity change increased the
number of allowed CPUs enough.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/20251119172550.280380631@linutronix.de

1 files changed, 0 insertions, 76 deletions

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 82c7978d548e..f9d0515db130 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -3745,83 +3745,7 @@ static inline void mm_cid_switch_to(struct task_struct *prev, struct task_struct
 	mm_cid_schedin(next);
 }
 
-/* Active implementation */
-static inline void init_sched_mm_cid(struct task_struct *t)
-{
-	struct mm_struct *mm = t->mm;
-	unsigned int max_cid;
-
-	if (!mm)
-		return;
-
-	/* Preset last_mm_cid */
-	max_cid = min_t(int, READ_ONCE(mm->mm_cid.nr_cpus_allowed), atomic_read(&mm->mm_users));
-	t->mm_cid.last_cid = max_cid - 1;
-}
-
-static inline bool __mm_cid_get(struct task_struct *t, unsigned int cid, unsigned int max_cids)
-{
-	struct mm_struct *mm = t->mm;
-
-	if (cid >= max_cids)
-		return false;
-	if (test_and_set_bit(cid, mm_cidmask(mm)))
-		return false;
-	t->mm_cid.cid = t->mm_cid.last_cid = cid;
-	__this_cpu_write(mm->mm_cid.pcpu->cid, cid);
-	return true;
-}
-
-static inline bool mm_cid_get(struct task_struct *t)
-{
-	struct mm_struct *mm = t->mm;
-	unsigned int max_cids;
-
-	max_cids = READ_ONCE(mm->mm_cid.max_cids);
-
-	/* Try to reuse the last CID of this task */
-	if (__mm_cid_get(t, t->mm_cid.last_cid, max_cids))
-		return true;
-
-	/* Try to reuse the last CID of this mm on this CPU */
-	if (__mm_cid_get(t, __this_cpu_read(mm->mm_cid.pcpu->cid), max_cids))
-		return true;
-
-	/* Try the first zero bit in the cidmask. */
-	return __mm_cid_get(t, find_first_zero_bit(mm_cidmask(mm), num_possible_cpus()), max_cids);
-}
-
-static inline void mm_cid_select(struct task_struct *t)
-{
-	/*
-	 * mm_cid_get() can fail when the maximum CID, which is determined
-	 * by min(mm->nr_cpus_allowed, mm->mm_users) changes concurrently.
-	 * That's a transient failure as there cannot be more tasks
-	 * concurrently on a CPU (or about to be scheduled in) than that.
-	 */
-	for (;;) {
-		if (mm_cid_get(t))
-			break;
-	}
-}
-
-static inline void switch_mm_cid(struct task_struct *prev, struct task_struct *next)
-{
-	if (prev->mm_cid.active) {
-		if (prev->mm_cid.cid != MM_CID_UNSET)
-			clear_bit(prev->mm_cid.cid, mm_cidmask(prev->mm));
-		prev->mm_cid.cid = MM_CID_UNSET;
-	}
-
-	if (next->mm_cid.active) {
-		mm_cid_select(next);
-		rseq_sched_set_task_mm_cid(next, next->mm_cid.cid);
-	}
-}
-
 #else /* !CONFIG_SCHED_MM_CID: */
-static inline void mm_cid_select(struct task_struct *t) { }
-static inline void switch_mm_cid(struct task_struct *prev, struct task_struct *next) { }
 static inline void mm_cid_switch_to(struct task_struct *prev, struct task_struct *next) { }
 #endif /* !CONFIG_SCHED_MM_CID */