[RFC PATCH 07/86] Revert "livepatch,sched: Add livepatch task switching to cond_resched()"
From: Ankur Arora
Date: Tue Nov 07 2023 - 16:59:48 EST
This reverts commit e3ff7c609f39671d1aaff4fb4a8594e14f3e03f8.
Note that removing this commit reintroduces "live patches failing to
complete within a reasonable amount of time due to CPU-bound kthreads."
Unfortunately this fix depends quite critically on PREEMPT_DYNAMIC and
existence of cond_resched() so this will need an alternate fix.
Signed-off-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
---
include/linux/livepatch.h | 1 -
include/linux/livepatch_sched.h | 29 ---------
include/linux/sched.h | 20 ++----
kernel/livepatch/core.c | 1 -
kernel/livepatch/transition.c | 107 +++++---------------------------
kernel/sched/core.c | 64 +++----------------
6 files changed, 28 insertions(+), 194 deletions(-)
delete mode 100644 include/linux/livepatch_sched.h
diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 9b9b38e89563..293e29960c6e 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -13,7 +13,6 @@
#include <linux/ftrace.h>
#include <linux/completion.h>
#include <linux/list.h>
-#include <linux/livepatch_sched.h>
#if IS_ENABLED(CONFIG_LIVEPATCH)
diff --git a/include/linux/livepatch_sched.h b/include/linux/livepatch_sched.h
deleted file mode 100644
index 013794fb5da0..000000000000
--- a/include/linux/livepatch_sched.h
+++ /dev/null
@@ -1,29 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-or-later */
-#ifndef _LINUX_LIVEPATCH_SCHED_H_
-#define _LINUX_LIVEPATCH_SCHED_H_
-
-#include <linux/jump_label.h>
-#include <linux/static_call_types.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)
-{
- if (static_branch_unlikely(&klp_sched_try_switch_key))
- __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) {}
-#endif /* CONFIG_LIVEPATCH */
-
-#endif /* _LINUX_LIVEPATCH_SCHED_H_ */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 5bdf80136e42..c5b0ef1ecfe4 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -36,7 +36,6 @@
#include <linux/seqlock.h>
#include <linux/kcsan.h>
#include <linux/rv.h>
-#include <linux/livepatch_sched.h>
#include <asm/kmap_size.h>
/* task_struct member predeclarations (sorted alphabetically): */
@@ -2087,9 +2086,6 @@ 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)
@@ -2098,7 +2094,6 @@ static __always_inline int _cond_resched(void)
}
#elif defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
-
extern int dynamic_cond_resched(void);
static __always_inline int _cond_resched(void)
@@ -2106,25 +2101,20 @@ static __always_inline int _cond_resched(void)
return dynamic_cond_resched();
}
-#else /* !CONFIG_PREEMPTION */
+#else
static inline int _cond_resched(void)
{
- klp_sched_try_switch();
return __cond_resched();
}
-#endif /* PREEMPT_DYNAMIC && CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
+#endif /* CONFIG_PREEMPT_DYNAMIC */
-#else /* CONFIG_PREEMPTION && !CONFIG_PREEMPT_DYNAMIC */
+#else
-static inline int _cond_resched(void)
-{
- klp_sched_try_switch();
- return 0;
-}
+static inline int _cond_resched(void) { return 0; }
-#endif /* !CONFIG_PREEMPTION || CONFIG_PREEMPT_DYNAMIC */
+#endif /* !defined(CONFIG_PREEMPTION) || defined(CONFIG_PREEMPT_DYNAMIC) */
#define cond_resched() ({ \
__might_resched(__FILE__, __LINE__, 0); \
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 61328328c474..fc851455740c 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -33,7 +33,6 @@
*
* - klp_ftrace_handler()
* - klp_update_patch_state()
- * - __klp_sched_try_switch()
*/
DEFINE_MUTEX(klp_mutex);
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index e54c3d60a904..70bc38f27af7 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -9,7 +9,6 @@
#include <linux/cpu.h>
#include <linux/stacktrace.h>
-#include <linux/static_call.h>
#include "core.h"
#include "patch.h"
#include "transition.h"
@@ -27,25 +26,6 @@ static int klp_target_state = KLP_UNDEFINED;
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.
- */
-#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 */
-
/*
* This work can be performed periodically to finish patching or unpatching any
* "straggler" tasks which failed to transition in the first attempt.
@@ -194,8 +174,8 @@ void klp_update_patch_state(struct task_struct *task)
* barrier (smp_rmb) for two cases:
*
* 1) Enforce the order of the TIF_PATCH_PENDING read and the
- * klp_target_state read. The corresponding write barriers are in
- * klp_init_transition() and klp_reverse_transition().
+ * klp_target_state read. The corresponding write barrier is in
+ * klp_init_transition().
*
* 2) Enforce the order of the TIF_PATCH_PENDING read and a future read
* of func->transition, if klp_ftrace_handler() is called later on
@@ -363,44 +343,6 @@ static bool klp_try_switch_task(struct task_struct *task)
return !ret;
}
-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.
- */
- preempt_disable();
-
- /*
- * Make sure current didn't get patched between the above check and
- * preempt_disable().
- */
- if (unlikely(!klp_patch_pending(current)))
- goto out;
-
- /*
- * Enforce the order of the TIF_PATCH_PENDING read above and the
- * klp_target_state read in klp_try_switch_task(). The corresponding
- * write barriers are in klp_init_transition() and
- * klp_reverse_transition().
- */
- 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.
* Kthreads with TIF_PATCH_PENDING set are woken up.
@@ -507,8 +449,7 @@ void klp_try_complete_transition(void)
return;
}
- /* Done! Now cleanup the data structures. */
- klp_cond_resched_disable();
+ /* we're done, now cleanup the data structures */
patch = klp_transition_patch;
klp_complete_transition();
@@ -560,8 +501,6 @@ void klp_start_transition(void)
set_tsk_thread_flag(task, TIF_PATCH_PENDING);
}
- klp_cond_resched_enable();
-
klp_signals_cnt = 0;
}
@@ -617,9 +556,8 @@ void klp_init_transition(struct klp_patch *patch, int state)
* see a func in transition with a task->patch_state of KLP_UNDEFINED.
*
* Also enforce the order of the klp_target_state write and future
- * TIF_PATCH_PENDING writes to ensure klp_update_patch_state() and
- * __klp_sched_try_switch() don't set a task->patch_state to
- * KLP_UNDEFINED.
+ * TIF_PATCH_PENDING writes to ensure klp_update_patch_state() doesn't
+ * set a task->patch_state to KLP_UNDEFINED.
*/
smp_wmb();
@@ -655,10 +593,14 @@ void klp_reverse_transition(void)
klp_target_state == KLP_PATCHED ? "patching to unpatching" :
"unpatching to patching");
+ klp_transition_patch->enabled = !klp_transition_patch->enabled;
+
+ klp_target_state = !klp_target_state;
+
/*
* Clear all TIF_PATCH_PENDING flags to prevent races caused by
- * klp_update_patch_state() or __klp_sched_try_switch() running in
- * parallel with the reverse transition.
+ * klp_update_patch_state() running in parallel with
+ * klp_start_transition().
*/
read_lock(&tasklist_lock);
for_each_process_thread(g, task)
@@ -668,28 +610,9 @@ void klp_reverse_transition(void)
for_each_possible_cpu(cpu)
clear_tsk_thread_flag(idle_task(cpu), TIF_PATCH_PENDING);
- /*
- * Make sure all existing invocations of klp_update_patch_state() and
- * __klp_sched_try_switch() see the cleared TIF_PATCH_PENDING before
- * starting the reverse transition.
- */
+ /* Let any remaining calls to klp_update_patch_state() complete */
klp_synchronize_transition();
- /*
- * All patching has stopped, now re-initialize the global variables to
- * prepare for the reverse transition.
- */
- klp_transition_patch->enabled = !klp_transition_patch->enabled;
- klp_target_state = !klp_target_state;
-
- /*
- * Enforce the order of the klp_target_state write and the
- * TIF_PATCH_PENDING writes in klp_start_transition() to ensure
- * klp_update_patch_state() and __klp_sched_try_switch() don't set
- * task->patch_state to the wrong value.
- */
- smp_wmb();
-
klp_start_transition();
}
@@ -703,9 +626,9 @@ void klp_copy_process(struct task_struct *child)
* the task flag up to date with the parent here.
*
* The operation is serialized against all klp_*_transition()
- * operations by the tasklist_lock. The only exceptions are
- * klp_update_patch_state(current) and __klp_sched_try_switch(), but we
- * cannot race with them because we are current.
+ * operations by the tasklist_lock. The only exception is
+ * klp_update_patch_state(current), but we cannot race with
+ * that because we are current.
*/
if (test_tsk_thread_flag(current, TIF_PATCH_PENDING))
set_tsk_thread_flag(child, TIF_PATCH_PENDING);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0e8764d63041..b43fda3c5733 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8597,7 +8597,6 @@ 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();
@@ -8746,17 +8745,13 @@ int sched_dynamic_mode(const char *str)
#error "Unsupported PREEMPT_DYNAMIC mechanism"
#endif
-DEFINE_MUTEX(sched_dynamic_mutex);
-static bool klp_override;
-
-static void __sched_dynamic_update(int mode)
+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);
@@ -8764,79 +8759,36 @@ 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);
preempt_dynamic_disable(irqentry_exit_cond_resched);
- if (mode != preempt_dynamic_mode)
- pr_info("Dynamic Preempt: none\n");
+ pr_info("Dynamic Preempt: none\n");
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);
preempt_dynamic_disable(irqentry_exit_cond_resched);
- if (mode != preempt_dynamic_mode)
- pr_info("Dynamic Preempt: voluntary\n");
+ pr_info("Dynamic Preempt: voluntary\n");
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);
preempt_dynamic_enable(irqentry_exit_cond_resched);
- if (mode != preempt_dynamic_mode)
- pr_info("Dynamic Preempt: full\n");
+ pr_info("Dynamic Preempt: full\n");
break;
}
preempt_dynamic_mode = mode;
}
-void sched_dynamic_update(int mode)
-{
- mutex_lock(&sched_dynamic_mutex);
- __sched_dynamic_update(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);
--
2.31.1