132 lines
3.8 KiB
Diff
132 lines
3.8 KiB
Diff
From 7af1b0bc40a20c1a44e4298081eaa2db43e5dac9 Mon Sep 17 00:00:00 2001
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From: Thomas Gleixner <tglx@linutronix.de>
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Date: Mon, 6 Jun 2011 12:20:33 +0200
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Subject: [PATCH 110/266] sched: Move mmdrop to RCU on RT
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.31-rt18.tar.xz
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Takes sleeping locks and calls into the memory allocator, so nothing
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we want to do in task switch and oder atomic contexts.
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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[bwh: Adjusted to apply on top of commit 6ff17bc5936e "coredump: fix race
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condition between mmget_not_zero()/get_task_mm() and core dumping"]
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---
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include/linux/mm_types.h | 4 ++++
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include/linux/sched/mm.h | 11 +++++++++++
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kernel/fork.c | 13 +++++++++++++
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kernel/sched/core.c | 18 ++++++++++++++++--
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4 files changed, 44 insertions(+), 2 deletions(-)
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--- a/include/linux/mm_types.h
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+++ b/include/linux/mm_types.h
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@@ -12,6 +12,7 @@
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#include <linux/completion.h>
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#include <linux/cpumask.h>
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#include <linux/uprobes.h>
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+#include <linux/rcupdate.h>
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#include <linux/page-flags-layout.h>
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#include <linux/workqueue.h>
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@@ -484,6 +485,9 @@ struct mm_struct {
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bool tlb_flush_batched;
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#endif
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struct uprobes_state uprobes_state;
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+#ifdef CONFIG_PREEMPT_RT_BASE
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+ struct rcu_head delayed_drop;
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+#endif
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#ifdef CONFIG_HUGETLB_PAGE
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atomic_long_t hugetlb_usage;
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#endif
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--- a/include/linux/sched/mm.h
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+++ b/include/linux/sched/mm.h
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@@ -49,6 +49,17 @@ static inline void mmdrop(struct mm_stru
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__mmdrop(mm);
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}
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+#ifdef CONFIG_PREEMPT_RT_BASE
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+extern void __mmdrop_delayed(struct rcu_head *rhp);
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+static inline void mmdrop_delayed(struct mm_struct *mm)
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+{
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+ if (atomic_dec_and_test(&mm->mm_count))
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+ call_rcu(&mm->delayed_drop, __mmdrop_delayed);
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+}
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+#else
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+# define mmdrop_delayed(mm) mmdrop(mm)
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+#endif
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+
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/*
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* This has to be called after a get_task_mm()/mmget_not_zero()
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* followed by taking the mmap_sem for writing before modifying the
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--- a/kernel/fork.c
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+++ b/kernel/fork.c
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@@ -642,6 +642,19 @@ void __mmdrop(struct mm_struct *mm)
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}
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EXPORT_SYMBOL_GPL(__mmdrop);
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+#ifdef CONFIG_PREEMPT_RT_BASE
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+/*
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+ * RCU callback for delayed mm drop. Not strictly rcu, but we don't
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+ * want another facility to make this work.
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+ */
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+void __mmdrop_delayed(struct rcu_head *rhp)
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+{
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+ struct mm_struct *mm = container_of(rhp, struct mm_struct, delayed_drop);
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+
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+ __mmdrop(mm);
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+}
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+#endif
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+
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static void mmdrop_async_fn(struct work_struct *work)
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{
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struct mm_struct *mm;
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--- a/kernel/sched/core.c
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+++ b/kernel/sched/core.c
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@@ -2729,9 +2729,13 @@ static struct rq *finish_task_switch(str
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* provided by mmdrop(),
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* - a sync_core for SYNC_CORE.
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*/
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+ /*
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+ * We use mmdrop_delayed() here so we don't have to do the
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+ * full __mmdrop() when we are the last user.
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+ */
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if (mm) {
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membarrier_mm_sync_core_before_usermode(mm);
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- mmdrop(mm);
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+ mmdrop_delayed(mm);
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}
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if (unlikely(prev_state == TASK_DEAD)) {
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if (prev->sched_class->task_dead)
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@@ -5560,6 +5564,8 @@ void sched_setnuma(struct task_struct *p
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#endif /* CONFIG_NUMA_BALANCING */
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#ifdef CONFIG_HOTPLUG_CPU
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+static DEFINE_PER_CPU(struct mm_struct *, idle_last_mm);
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+
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/*
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* Ensure that the idle task is using init_mm right before its CPU goes
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* offline.
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@@ -5575,7 +5581,11 @@ void idle_task_exit(void)
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current->active_mm = &init_mm;
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finish_arch_post_lock_switch();
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}
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- mmdrop(mm);
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+ /*
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+ * Defer the cleanup to an alive cpu. On RT we can neither
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+ * call mmdrop() nor mmdrop_delayed() from here.
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+ */
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+ per_cpu(idle_last_mm, smp_processor_id()) = mm;
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}
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/*
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@@ -5887,6 +5897,10 @@ int sched_cpu_dying(unsigned int cpu)
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update_max_interval();
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nohz_balance_exit_idle(rq);
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hrtick_clear(rq);
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+ if (per_cpu(idle_last_mm, cpu)) {
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+ mmdrop_delayed(per_cpu(idle_last_mm, cpu));
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+ per_cpu(idle_last_mm, cpu) = NULL;
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+ }
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return 0;
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}
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#endif
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