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Subject[GIT pull] timers/urgent for v5.16-rc1
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Linus,

please pull the latest timers/urgent branch from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git timers-urgent-2021-11-14

up to: ca7752caeaa7: posix-cpu-timers: Clear task::posix_cputimers_work in copy_process()

A single fix for POSIX CPU timers to address a problem where POSIX CPU
timer delivery stops working for a new child task because copy_process()
copies state information which is only valid for the parent task.

Thanks,

tglx

------------------>
Michael Pratt (1):
posix-cpu-timers: Clear task::posix_cputimers_work in copy_process()


include/linux/posix-timers.h | 2 ++
kernel/fork.c | 1 +
kernel/time/posix-cpu-timers.c | 19 +++++++++++++++++--
3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h
index 00fef0064355..5bbcd280bfd2 100644
--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -184,8 +184,10 @@ static inline void posix_cputimers_group_init(struct posix_cputimers *pct,
#endif

#ifdef CONFIG_POSIX_CPU_TIMERS_TASK_WORK
+void clear_posix_cputimers_work(struct task_struct *p);
void posix_cputimers_init_work(void);
#else
+static inline void clear_posix_cputimers_work(struct task_struct *p) { }
static inline void posix_cputimers_init_work(void) { }
#endif

diff --git a/kernel/fork.c b/kernel/fork.c
index 8e9feeef555e..8269ae2e5d7c 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2279,6 +2279,7 @@ static __latent_entropy struct task_struct *copy_process(
p->pdeath_signal = 0;
INIT_LIST_HEAD(&p->thread_group);
p->task_works = NULL;
+ clear_posix_cputimers_work(p);

#ifdef CONFIG_KRETPROBES
p->kretprobe_instances.first = NULL;
diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 643d412ac623..96b4e7810426 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -1158,14 +1158,29 @@ static void posix_cpu_timers_work(struct callback_head *work)
handle_posix_cpu_timers(current);
}

+/*
+ * Clear existing posix CPU timers task work.
+ */
+void clear_posix_cputimers_work(struct task_struct *p)
+{
+ /*
+ * A copied work entry from the old task is not meaningful, clear it.
+ * N.B. init_task_work will not do this.
+ */
+ memset(&p->posix_cputimers_work.work, 0,
+ sizeof(p->posix_cputimers_work.work));
+ init_task_work(&p->posix_cputimers_work.work,
+ posix_cpu_timers_work);
+ p->posix_cputimers_work.scheduled = false;
+}
+
/*
* Initialize posix CPU timers task work in init task. Out of line to
* keep the callback static and to avoid header recursion hell.
*/
void __init posix_cputimers_init_work(void)
{
- init_task_work(&current->posix_cputimers_work.work,
- posix_cpu_timers_work);
+ clear_posix_cputimers_work(current);
}

/*
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