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Message-ID: <174722200203.406.16353479744714543012.tip-bot2@tip-bot2>
Date: Wed, 14 May 2025 11:26:42 -0000
From: "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Thomas Gleixner <tglx@...utronix.de>, Petr Mladek <pmladek@...e.com>,
Miroslav Benes <mbenes@...e.cz>, Josh Poimboeuf <jpoimboe@...nel.org>,
x86@...nel.org, linux-kernel@...r.kernel.org
Subject:
[tip: sched/core] sched,livepatch: Untangle cond_resched() and live-patching
The following commit has been merged into the sched/core branch of tip:
Commit-ID: 676e8cf70cb0533e1118e29898c9a9c33ae3a10f
Gitweb: https://git.kernel.org/tip/676e8cf70cb0533e1118e29898c9a9c33ae3a10f
Author: Peter Zijlstra <peterz@...radead.org>
AuthorDate: Fri, 09 May 2025 13:36:59 +02:00
Committer: Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 14 May 2025 13:16:24 +02:00
sched,livepatch: Untangle cond_resched() and live-patching
With the goal of deprecating / removing VOLUNTARY preempt, live-patch
needs to stop relying on cond_resched() to make forward progress.
Instead, rely on schedule() with TASK_FREEZABLE set. Just like
live-patching, the freezer needs to be able to stop tasks in a safe /
known state.
[bigeasy: use likely() in __klp_sched_try_switch() and update comments]
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Petr Mladek <pmladek@...e.com>
Tested-by: Petr Mladek <pmladek@...e.com>
Tested-by: Miroslav Benes <mbenes@...e.cz>
Acked-by: Miroslav Benes <mbenes@...e.cz>
Acked-by: Josh Poimboeuf <jpoimboe@...nel.org>
Link: https://lore.kernel.org/r/20250509113659.wkP_HJ5z@linutronix.de
---
include/linux/livepatch_sched.h | 14 +++------
include/linux/sched.h | 6 +----
kernel/livepatch/transition.c | 49 ++++++++-----------------------
kernel/sched/core.c | 50 +++++---------------------------
4 files changed, 27 insertions(+), 92 deletions(-)
diff --git a/include/linux/livepatch_sched.h b/include/linux/livepatch_sched.h
index 013794f..065c185 100644
--- a/include/linux/livepatch_sched.h
+++ b/include/linux/livepatch_sched.h
@@ -3,27 +3,23 @@
#define _LINUX_LIVEPATCH_SCHED_H_
#include <linux/jump_label.h>
-#include <linux/static_call_types.h>
+#include <linux/sched.h>
#ifdef CONFIG_LIVEPATCH
void __klp_sched_try_switch(void);
-#if !defined(CONFIG_PREEMPT_DYNAMIC) || !defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
-
DECLARE_STATIC_KEY_FALSE(klp_sched_try_switch_key);
-static __always_inline void klp_sched_try_switch(void)
+static __always_inline void klp_sched_try_switch(struct task_struct *curr)
{
- if (static_branch_unlikely(&klp_sched_try_switch_key))
+ if (static_branch_unlikely(&klp_sched_try_switch_key) &&
+ READ_ONCE(curr->__state) & TASK_FREEZABLE)
__klp_sched_try_switch();
}
-#endif /* !CONFIG_PREEMPT_DYNAMIC || !CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
-
#else /* !CONFIG_LIVEPATCH */
-static inline void klp_sched_try_switch(void) {}
-static inline void __klp_sched_try_switch(void) {}
+static inline void klp_sched_try_switch(struct task_struct *curr) {}
#endif /* CONFIG_LIVEPATCH */
#endif /* _LINUX_LIVEPATCH_SCHED_H_ */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f96ac19..b981959 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -44,7 +44,6 @@
#include <linux/seqlock_types.h>
#include <linux/kcsan.h>
#include <linux/rv.h>
-#include <linux/livepatch_sched.h>
#include <linux/uidgid_types.h>
#include <linux/tracepoint-defs.h>
#include <asm/kmap_size.h>
@@ -2089,9 +2088,6 @@ extern int __cond_resched(void);
#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
-void sched_dynamic_klp_enable(void);
-void sched_dynamic_klp_disable(void);
-
DECLARE_STATIC_CALL(cond_resched, __cond_resched);
static __always_inline int _cond_resched(void)
@@ -2112,7 +2108,6 @@ static __always_inline int _cond_resched(void)
static inline int _cond_resched(void)
{
- klp_sched_try_switch();
return __cond_resched();
}
@@ -2122,7 +2117,6 @@ static inline int _cond_resched(void)
static inline int _cond_resched(void)
{
- klp_sched_try_switch();
return 0;
}
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index ba06945..2351a19 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -29,22 +29,13 @@ static unsigned int klp_signals_cnt;
/*
* When a livepatch is in progress, enable klp stack checking in
- * cond_resched(). This helps CPU-bound kthreads get patched.
+ * schedule(). This helps CPU-bound kthreads get patched.
*/
-#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
-
-#define klp_cond_resched_enable() sched_dynamic_klp_enable()
-#define klp_cond_resched_disable() sched_dynamic_klp_disable()
-
-#else /* !CONFIG_PREEMPT_DYNAMIC || !CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
DEFINE_STATIC_KEY_FALSE(klp_sched_try_switch_key);
-EXPORT_SYMBOL(klp_sched_try_switch_key);
-#define klp_cond_resched_enable() static_branch_enable(&klp_sched_try_switch_key)
-#define klp_cond_resched_disable() static_branch_disable(&klp_sched_try_switch_key)
-
-#endif /* CONFIG_PREEMPT_DYNAMIC && CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
+#define klp_resched_enable() static_branch_enable(&klp_sched_try_switch_key)
+#define klp_resched_disable() static_branch_disable(&klp_sched_try_switch_key)
/*
* This work can be performed periodically to finish patching or unpatching any
@@ -365,26 +356,18 @@ static bool klp_try_switch_task(struct task_struct *task)
void __klp_sched_try_switch(void)
{
- if (likely(!klp_patch_pending(current)))
- return;
-
/*
- * This function is called from cond_resched() which is called in many
- * places throughout the kernel. Using the klp_mutex here might
- * deadlock.
- *
- * Instead, disable preemption to prevent racing with other callers of
- * klp_try_switch_task(). Thanks to task_call_func() they won't be
- * able to switch this task while it's running.
+ * This function is called from __schedule() while a context switch is
+ * about to happen. Preemption is already disabled and klp_mutex
+ * can't be acquired.
+ * Disabled preemption is used to prevent racing with other callers of
+ * klp_try_switch_task(). Thanks to task_call_func() they won't be
+ * able to switch to this task while it's running.
*/
- preempt_disable();
+ lockdep_assert_preemption_disabled();
- /*
- * Make sure current didn't get patched between the above check and
- * preempt_disable().
- */
- if (unlikely(!klp_patch_pending(current)))
- goto out;
+ if (likely(!klp_patch_pending(current)))
+ return;
/*
* Enforce the order of the TIF_PATCH_PENDING read above and the
@@ -395,11 +378,7 @@ void __klp_sched_try_switch(void)
smp_rmb();
klp_try_switch_task(current);
-
-out:
- preempt_enable();
}
-EXPORT_SYMBOL(__klp_sched_try_switch);
/*
* Sends a fake signal to all non-kthread tasks with TIF_PATCH_PENDING set.
@@ -508,7 +487,7 @@ void klp_try_complete_transition(void)
}
/* Done! Now cleanup the data structures. */
- klp_cond_resched_disable();
+ klp_resched_disable();
patch = klp_transition_patch;
klp_complete_transition();
@@ -560,7 +539,7 @@ void klp_start_transition(void)
set_tsk_thread_flag(task, TIF_PATCH_PENDING);
}
- klp_cond_resched_enable();
+ klp_resched_enable();
klp_signals_cnt = 0;
}
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a3507ed..bece0ba 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -66,6 +66,7 @@
#include <linux/vtime.h>
#include <linux/wait_api.h>
#include <linux/workqueue_api.h>
+#include <linux/livepatch_sched.h>
#ifdef CONFIG_PREEMPT_DYNAMIC
# ifdef CONFIG_GENERIC_ENTRY
@@ -6676,6 +6677,8 @@ static void __sched notrace __schedule(int sched_mode)
if (sched_feat(HRTICK) || sched_feat(HRTICK_DL))
hrtick_clear(rq);
+ klp_sched_try_switch(prev);
+
local_irq_disable();
rcu_note_context_switch(preempt);
@@ -7336,7 +7339,6 @@ EXPORT_STATIC_CALL_TRAMP(might_resched);
static DEFINE_STATIC_KEY_FALSE(sk_dynamic_cond_resched);
int __sched dynamic_cond_resched(void)
{
- klp_sched_try_switch();
if (!static_branch_unlikely(&sk_dynamic_cond_resched))
return 0;
return __cond_resched();
@@ -7508,7 +7510,6 @@ int sched_dynamic_mode(const char *str)
#endif
static DEFINE_MUTEX(sched_dynamic_mutex);
-static bool klp_override;
static void __sched_dynamic_update(int mode)
{
@@ -7516,8 +7517,7 @@ static void __sched_dynamic_update(int mode)
* Avoid {NONE,VOLUNTARY} -> FULL transitions from ever ending up in
* the ZERO state, which is invalid.
*/
- if (!klp_override)
- preempt_dynamic_enable(cond_resched);
+ preempt_dynamic_enable(cond_resched);
preempt_dynamic_enable(might_resched);
preempt_dynamic_enable(preempt_schedule);
preempt_dynamic_enable(preempt_schedule_notrace);
@@ -7526,8 +7526,7 @@ static void __sched_dynamic_update(int mode)
switch (mode) {
case preempt_dynamic_none:
- if (!klp_override)
- preempt_dynamic_enable(cond_resched);
+ preempt_dynamic_enable(cond_resched);
preempt_dynamic_disable(might_resched);
preempt_dynamic_disable(preempt_schedule);
preempt_dynamic_disable(preempt_schedule_notrace);
@@ -7538,8 +7537,7 @@ static void __sched_dynamic_update(int mode)
break;
case preempt_dynamic_voluntary:
- if (!klp_override)
- preempt_dynamic_enable(cond_resched);
+ preempt_dynamic_enable(cond_resched);
preempt_dynamic_enable(might_resched);
preempt_dynamic_disable(preempt_schedule);
preempt_dynamic_disable(preempt_schedule_notrace);
@@ -7550,8 +7548,7 @@ static void __sched_dynamic_update(int mode)
break;
case preempt_dynamic_full:
- if (!klp_override)
- preempt_dynamic_disable(cond_resched);
+ preempt_dynamic_disable(cond_resched);
preempt_dynamic_disable(might_resched);
preempt_dynamic_enable(preempt_schedule);
preempt_dynamic_enable(preempt_schedule_notrace);
@@ -7562,8 +7559,7 @@ static void __sched_dynamic_update(int mode)
break;
case preempt_dynamic_lazy:
- if (!klp_override)
- preempt_dynamic_disable(cond_resched);
+ preempt_dynamic_disable(cond_resched);
preempt_dynamic_disable(might_resched);
preempt_dynamic_enable(preempt_schedule);
preempt_dynamic_enable(preempt_schedule_notrace);
@@ -7584,36 +7580,6 @@ void sched_dynamic_update(int mode)
mutex_unlock(&sched_dynamic_mutex);
}
-#ifdef CONFIG_HAVE_PREEMPT_DYNAMIC_CALL
-
-static int klp_cond_resched(void)
-{
- __klp_sched_try_switch();
- return __cond_resched();
-}
-
-void sched_dynamic_klp_enable(void)
-{
- mutex_lock(&sched_dynamic_mutex);
-
- klp_override = true;
- static_call_update(cond_resched, klp_cond_resched);
-
- mutex_unlock(&sched_dynamic_mutex);
-}
-
-void sched_dynamic_klp_disable(void)
-{
- mutex_lock(&sched_dynamic_mutex);
-
- klp_override = false;
- __sched_dynamic_update(preempt_dynamic_mode);
-
- mutex_unlock(&sched_dynamic_mutex);
-}
-
-#endif /* CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
-
static int __init setup_preempt_mode(char *str)
{
int mode = sched_dynamic_mode(str);
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