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Date: Mon, 22 Jun 2015 10:44:30 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: Linus Torvalds <torvalds@...ux-foundation.org>
cc: LKML <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Ingo Molnar <mingo@...nel.org>,
"H. Peter Anvin" <hpa@...or.com>,
Peter Zijlstra <peterz@...radead.org>
Subject: [GIT pull] NOHZ changes for 4.2
Linus,
please pull the latest timers-nohz-for-linus git tree from:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git timers-nohz-for-linus
A few updates to the nohz infrastructure:
- Recursion protection for context tracking
- Make the TIF_NOHZ inheritance smarter
- Isolate cpus which belong to the NOHZ full set
Thanks,
tglx
------------------>
Chris Metcalf (2):
nohz: Add tick_nohz_full_add_cpus_to() API
nohz: Set isolcpus when nohz_full is set
Frederic Weisbecker (2):
context_tracking: Protect against recursion
context_tracking: Inherit TIF_NOHZ through forks instead of context switches
include/linux/context_tracking.h | 10 -----
include/linux/context_tracking_state.h | 1 +
include/linux/sched.h | 3 ++
include/linux/tick.h | 7 ++++
kernel/context_tracking.c | 67 +++++++++++++++++++++++-----------
kernel/sched/core.c | 4 +-
6 files changed, 59 insertions(+), 33 deletions(-)
diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index 2821838256b4..b96bd299966f 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -14,8 +14,6 @@ extern void context_tracking_enter(enum ctx_state state);
extern void context_tracking_exit(enum ctx_state state);
extern void context_tracking_user_enter(void);
extern void context_tracking_user_exit(void);
-extern void __context_tracking_task_switch(struct task_struct *prev,
- struct task_struct *next);
static inline void user_enter(void)
{
@@ -51,19 +49,11 @@ static inline void exception_exit(enum ctx_state prev_ctx)
}
}
-static inline void context_tracking_task_switch(struct task_struct *prev,
- struct task_struct *next)
-{
- if (context_tracking_is_enabled())
- __context_tracking_task_switch(prev, next);
-}
#else
static inline void user_enter(void) { }
static inline void user_exit(void) { }
static inline enum ctx_state exception_enter(void) { return 0; }
static inline void exception_exit(enum ctx_state prev_ctx) { }
-static inline void context_tracking_task_switch(struct task_struct *prev,
- struct task_struct *next) { }
#endif /* !CONFIG_CONTEXT_TRACKING */
diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h
index 6b7b96a32b75..678ecdf90cf6 100644
--- a/include/linux/context_tracking_state.h
+++ b/include/linux/context_tracking_state.h
@@ -12,6 +12,7 @@ struct context_tracking {
* may be further optimized using static keys.
*/
bool active;
+ int recursion;
enum ctx_state {
CONTEXT_KERNEL = 0,
CONTEXT_USER,
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 26a2e6122734..185a750e4ed4 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2532,6 +2532,9 @@ static inline unsigned long wait_task_inactive(struct task_struct *p,
}
#endif
+#define tasklist_empty() \
+ list_empty(&init_task.tasks)
+
#define next_task(p) \
list_entry_rcu((p)->tasks.next, struct task_struct, tasks)
diff --git a/include/linux/tick.h b/include/linux/tick.h
index f8492da57ad3..4191b5623a28 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -134,6 +134,12 @@ static inline bool tick_nohz_full_cpu(int cpu)
return cpumask_test_cpu(cpu, tick_nohz_full_mask);
}
+static inline void tick_nohz_full_add_cpus_to(struct cpumask *mask)
+{
+ if (tick_nohz_full_enabled())
+ cpumask_or(mask, mask, tick_nohz_full_mask);
+}
+
extern void __tick_nohz_full_check(void);
extern void tick_nohz_full_kick(void);
extern void tick_nohz_full_kick_cpu(int cpu);
@@ -142,6 +148,7 @@ extern void __tick_nohz_task_switch(struct task_struct *tsk);
#else
static inline bool tick_nohz_full_enabled(void) { return false; }
static inline bool tick_nohz_full_cpu(int cpu) { return false; }
+static inline void tick_nohz_full_add_cpus_to(struct cpumask *mask) { }
static inline void __tick_nohz_full_check(void) { }
static inline void tick_nohz_full_kick_cpu(int cpu) { }
static inline void tick_nohz_full_kick(void) { }
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 72d59a1a6eb6..0a495ab35bc7 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -30,12 +30,23 @@ EXPORT_SYMBOL_GPL(context_tracking_enabled);
DEFINE_PER_CPU(struct context_tracking, context_tracking);
EXPORT_SYMBOL_GPL(context_tracking);
-void context_tracking_cpu_set(int cpu)
+static bool context_tracking_recursion_enter(void)
{
- if (!per_cpu(context_tracking.active, cpu)) {
- per_cpu(context_tracking.active, cpu) = true;
- static_key_slow_inc(&context_tracking_enabled);
- }
+ int recursion;
+
+ recursion = __this_cpu_inc_return(context_tracking.recursion);
+ if (recursion == 1)
+ return true;
+
+ WARN_ONCE((recursion < 1), "Invalid context tracking recursion value %d\n", recursion);
+ __this_cpu_dec(context_tracking.recursion);
+
+ return false;
+}
+
+static void context_tracking_recursion_exit(void)
+{
+ __this_cpu_dec(context_tracking.recursion);
}
/**
@@ -75,6 +86,9 @@ void context_tracking_enter(enum ctx_state state)
WARN_ON_ONCE(!current->mm);
local_irq_save(flags);
+ if (!context_tracking_recursion_enter())
+ goto out_irq_restore;
+
if ( __this_cpu_read(context_tracking.state) != state) {
if (__this_cpu_read(context_tracking.active)) {
/*
@@ -105,6 +119,8 @@ void context_tracking_enter(enum ctx_state state)
*/
__this_cpu_write(context_tracking.state, state);
}
+ context_tracking_recursion_exit();
+out_irq_restore:
local_irq_restore(flags);
}
NOKPROBE_SYMBOL(context_tracking_enter);
@@ -139,6 +155,9 @@ void context_tracking_exit(enum ctx_state state)
return;
local_irq_save(flags);
+ if (!context_tracking_recursion_enter())
+ goto out_irq_restore;
+
if (__this_cpu_read(context_tracking.state) == state) {
if (__this_cpu_read(context_tracking.active)) {
/*
@@ -153,6 +172,8 @@ void context_tracking_exit(enum ctx_state state)
}
__this_cpu_write(context_tracking.state, CONTEXT_KERNEL);
}
+ context_tracking_recursion_exit();
+out_irq_restore:
local_irq_restore(flags);
}
NOKPROBE_SYMBOL(context_tracking_exit);
@@ -164,24 +185,26 @@ void context_tracking_user_exit(void)
}
NOKPROBE_SYMBOL(context_tracking_user_exit);
-/**
- * __context_tracking_task_switch - context switch the syscall callbacks
- * @prev: the task that is being switched out
- * @next: the task that is being switched in
- *
- * The context tracking uses the syscall slow path to implement its user-kernel
- * boundaries probes on syscalls. This way it doesn't impact the syscall fast
- * path on CPUs that don't do context tracking.
- *
- * But we need to clear the flag on the previous task because it may later
- * migrate to some CPU that doesn't do the context tracking. As such the TIF
- * flag may not be desired there.
- */
-void __context_tracking_task_switch(struct task_struct *prev,
- struct task_struct *next)
+void __init context_tracking_cpu_set(int cpu)
{
- clear_tsk_thread_flag(prev, TIF_NOHZ);
- set_tsk_thread_flag(next, TIF_NOHZ);
+ static __initdata bool initialized = false;
+
+ if (!per_cpu(context_tracking.active, cpu)) {
+ per_cpu(context_tracking.active, cpu) = true;
+ static_key_slow_inc(&context_tracking_enabled);
+ }
+
+ if (initialized)
+ return;
+
+ /*
+ * Set TIF_NOHZ to init/0 and let it propagate to all tasks through fork
+ * This assumes that init is the only task at this early boot stage.
+ */
+ set_tsk_thread_flag(&init_task, TIF_NOHZ);
+ WARN_ON_ONCE(!tasklist_empty());
+
+ initialized = true;
}
#ifdef CONFIG_CONTEXT_TRACKING_FORCE
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index fe22f7510bce..b8f48763579b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2332,7 +2332,6 @@ context_switch(struct rq *rq, struct task_struct *prev,
*/
spin_release(&rq->lock.dep_map, 1, _THIS_IP_);
- context_tracking_task_switch(prev, next);
/* Here we just switch the register state and the stack. */
switch_to(prev, next, prev);
barrier();
@@ -7037,6 +7036,9 @@ void __init sched_init_smp(void)
alloc_cpumask_var(&non_isolated_cpus, GFP_KERNEL);
alloc_cpumask_var(&fallback_doms, GFP_KERNEL);
+ /* nohz_full won't take effect without isolating the cpus. */
+ tick_nohz_full_add_cpus_to(cpu_isolated_map);
+
sched_init_numa();
/*
--
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