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Message-Id: <20201214065312.270062-2-npiggin@gmail.com>
Date: Mon, 14 Dec 2020 16:53:08 +1000
From: Nicholas Piggin <npiggin@...il.com>
To: linux-kernel@...r.kernel.org
Cc: Nicholas Piggin <npiggin@...il.com>, linux-arch@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org,
Anton Blanchard <anton@...abs.org>,
Andy Lutomirski <luto@...nel.org>
Subject: [PATCH v2 1/5] lazy tlb: introduce lazy mm refcount helper functions
Add explicit _lazy_tlb annotated functions for lazy mm refcounting.
This makes things a bit more explicit, and allows explicit refcounting
to be removed if it is not used.
Signed-off-by: Nicholas Piggin <npiggin@...il.com>
---
arch/arm/mach-rpc/ecard.c | 2 +-
arch/powerpc/mm/book3s64/radix_tlb.c | 4 ++--
fs/exec.c | 4 ++--
include/linux/sched/mm.h | 11 +++++++++++
kernel/cpu.c | 2 +-
kernel/exit.c | 2 +-
kernel/kthread.c | 11 +++++++----
kernel/sched/core.c | 15 ++++++++-------
8 files changed, 33 insertions(+), 18 deletions(-)
diff --git a/arch/arm/mach-rpc/ecard.c b/arch/arm/mach-rpc/ecard.c
index 827b50f1c73e..1b4a41aad793 100644
--- a/arch/arm/mach-rpc/ecard.c
+++ b/arch/arm/mach-rpc/ecard.c
@@ -253,7 +253,7 @@ static int ecard_init_mm(void)
current->mm = mm;
current->active_mm = mm;
activate_mm(active_mm, mm);
- mmdrop(active_mm);
+ mmdrop_lazy_tlb(active_mm);
ecard_init_pgtables(mm);
return 0;
}
diff --git a/arch/powerpc/mm/book3s64/radix_tlb.c b/arch/powerpc/mm/book3s64/radix_tlb.c
index b487b489d4b6..74708aef333e 100644
--- a/arch/powerpc/mm/book3s64/radix_tlb.c
+++ b/arch/powerpc/mm/book3s64/radix_tlb.c
@@ -658,10 +658,10 @@ static void do_exit_flush_lazy_tlb(void *arg)
if (current->active_mm == mm) {
WARN_ON_ONCE(current->mm != NULL);
/* Is a kernel thread and is using mm as the lazy tlb */
- mmgrab(&init_mm);
+ mmgrab_lazy_tlb(&init_mm);
current->active_mm = &init_mm;
switch_mm_irqs_off(mm, &init_mm, current);
- mmdrop(mm);
+ mmdrop_lazy_tlb(mm);
}
atomic_dec(&mm->context.active_cpus);
diff --git a/fs/exec.c b/fs/exec.c
index 547a2390baf5..56fc23dcbe4d 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1028,9 +1028,9 @@ static int exec_mmap(struct mm_struct *mm)
setmax_mm_hiwater_rss(&tsk->signal->maxrss, old_mm);
mm_update_next_owner(old_mm);
mmput(old_mm);
- return 0;
+ } else {
+ mmdrop_lazy_tlb(active_mm);
}
- mmdrop(active_mm);
return 0;
}
diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index d5ece7a9a403..94a117160083 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -49,6 +49,17 @@ static inline void mmdrop(struct mm_struct *mm)
__mmdrop(mm);
}
+/* Helpers for lazy TLB mm refcounting */
+static inline void mmgrab_lazy_tlb(struct mm_struct *mm)
+{
+ mmgrab(mm);
+}
+
+static inline void mmdrop_lazy_tlb(struct mm_struct *mm)
+{
+ mmdrop(mm);
+}
+
/**
* mmget() - Pin the address space associated with a &struct mm_struct.
* @mm: The address space to pin.
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 2b8d7a5db383..a54cdfa08d71 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -576,7 +576,7 @@ static int finish_cpu(unsigned int cpu)
*/
if (mm != &init_mm)
idle->active_mm = &init_mm;
- mmdrop(mm);
+ mmdrop_lazy_tlb(mm);
return 0;
}
diff --git a/kernel/exit.c b/kernel/exit.c
index 1f236ed375f8..3711a74fcf4a 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -474,7 +474,7 @@ static void exit_mm(void)
__set_current_state(TASK_RUNNING);
mmap_read_lock(mm);
}
- mmgrab(mm);
+ mmgrab_lazy_tlb(mm);
BUG_ON(mm != current->active_mm);
/* more a memory barrier than a real lock */
task_lock(current);
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 933a625621b8..da189e0d26ed 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -1240,14 +1240,14 @@ void kthread_use_mm(struct mm_struct *mm)
WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD));
WARN_ON_ONCE(tsk->mm);
+ mmgrab(mm);
+
task_lock(tsk);
/* Hold off tlb flush IPIs while switching mm's */
local_irq_disable();
active_mm = tsk->active_mm;
- if (active_mm != mm) {
- mmgrab(mm);
+ if (active_mm != mm)
tsk->active_mm = mm;
- }
tsk->mm = mm;
switch_mm_irqs_off(active_mm, mm, tsk);
local_irq_enable();
@@ -1257,7 +1257,7 @@ void kthread_use_mm(struct mm_struct *mm)
#endif
if (active_mm != mm)
- mmdrop(active_mm);
+ mmdrop_lazy_tlb(active_mm);
to_kthread(tsk)->oldfs = force_uaccess_begin();
}
@@ -1280,10 +1280,13 @@ void kthread_unuse_mm(struct mm_struct *mm)
sync_mm_rss(mm);
local_irq_disable();
tsk->mm = NULL;
+ mmgrab_lazy_tlb(mm);
/* active_mm is still 'mm' */
enter_lazy_tlb(mm, tsk);
local_irq_enable();
task_unlock(tsk);
+
+ mmdrop(mm);
}
EXPORT_SYMBOL_GPL(kthread_unuse_mm);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e7e453492cff..c2f8ea43d29b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3629,13 +3629,14 @@ static struct rq *finish_task_switch(struct task_struct *prev)
* rq->curr, before returning to userspace, so provide them here:
*
* - a full memory barrier for {PRIVATE,GLOBAL}_EXPEDITED, implicitly
- * provided by mmdrop(),
+ * provided by mmdrop_lazy_tlb(),
* - a sync_core for SYNC_CORE.
*/
if (mm) {
membarrier_mm_sync_core_before_usermode(mm);
- mmdrop(mm);
+ mmdrop_lazy_tlb(mm);
}
+
if (unlikely(prev_state == TASK_DEAD)) {
if (prev->sched_class->task_dead)
prev->sched_class->task_dead(prev);
@@ -3739,9 +3740,9 @@ context_switch(struct rq *rq, struct task_struct *prev,
/*
* kernel -> kernel lazy + transfer active
- * user -> kernel lazy + mmgrab() active
+ * user -> kernel lazy + mmgrab_lazy_tlb() active
*
- * kernel -> user switch + mmdrop() active
+ * kernel -> user switch + mmdrop_lazy_tlb() active
* user -> user switch
*/
if (!next->mm) { // to kernel
@@ -3749,7 +3750,7 @@ context_switch(struct rq *rq, struct task_struct *prev,
next->active_mm = prev->active_mm;
if (prev->mm) // from user
- mmgrab(prev->active_mm);
+ mmgrab_lazy_tlb(prev->active_mm);
else
prev->active_mm = NULL;
} else { // to user
@@ -3765,7 +3766,7 @@ context_switch(struct rq *rq, struct task_struct *prev,
switch_mm_irqs_off(prev->active_mm, next->mm, next);
if (!prev->mm) { // from kernel
- /* will mmdrop() in finish_task_switch(). */
+ /* will mmdrop_lazy_tlb() in finish_task_switch(). */
rq->prev_mm = prev->active_mm;
prev->active_mm = NULL;
}
@@ -7206,7 +7207,7 @@ void __init sched_init(void)
/*
* The boot idle thread does lazy MMU switching as well:
*/
- mmgrab(&init_mm);
+ mmgrab_lazy_tlb(&init_mm);
enter_lazy_tlb(&init_mm, current);
/*
--
2.23.0
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