Merge tag 'timers-urgent-2024-11-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull timer fix from Thomas Gleixner:
 "A single fix for posix CPU timers.

  When a thread is cloned, the posix CPU timers are not inherited.

  If the parent has a CPU timer armed the corresponding tick dependency
  in the tasks tick_dep_mask is set and copied to the new thread, which
  means the new thread and all decendants will prevent the system to go
  into full NOHZ operation.

  Clear the tick dependency mask in copy_process() to fix this"

* tag 'timers-urgent-2024-11-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  posix-cpu-timers: Clear TICK_DEP_BIT_POSIX_TIMER on clone

Author: torvalds

include/linux/tick.h

@@ -251,12 +251,19 @@ static inline void tick_dep_set_task(struct task_struct *tsk,
 	if (tick_nohz_full_enabled())
 		tick_nohz_dep_set_task(tsk, bit);
 }
+
 static inline void tick_dep_clear_task(struct task_struct *tsk,
 				       enum tick_dep_bits bit)
 {
 	if (tick_nohz_full_enabled())
 		tick_nohz_dep_clear_task(tsk, bit);
 }
+
+static inline void tick_dep_init_task(struct task_struct *tsk)
+{
+	atomic_set(&tsk->tick_dep_mask, 0);
+}
+
 static inline void tick_dep_set_signal(struct task_struct *tsk,
 				       enum tick_dep_bits bit)
 {
@@ -290,6 +297,7 @@ static inline void tick_dep_set_task(struct task_struct *tsk,
 				     enum tick_dep_bits bit) { }
 static inline void tick_dep_clear_task(struct task_struct *tsk,
 				       enum tick_dep_bits bit) { }
+static inline void tick_dep_init_task(struct task_struct *tsk) { }
 static inline void tick_dep_set_signal(struct task_struct *tsk,
 				       enum tick_dep_bits bit) { }
 static inline void tick_dep_clear_signal(struct signal_struct *signal,

kernel/fork.c

@@ -105,6 +105,7 @@
 #include <linux/rseq.h>
 #include <uapi/linux/pidfd.h>
 #include <linux/pidfs.h>
+#include <linux/tick.h>
 
 #include <asm/pgalloc.h>
 #include <linux/uaccess.h>
@@ -2292,6 +2293,7 @@ __latent_entropy struct task_struct *copy_process(
 	acct_clear_integrals(p);
 
 	posix_cputimers_init(&p->posix_cputimers);
+	tick_dep_init_task(p);
 
 	p->io_context = NULL;
 	audit_set_context(p, NULL);