There have been reports [1][2] of live patches failing to complete within a reasonable amount of time due to CPU-bound kthreads. Fix it by patching tasks in cond_resched(). There are four different flavors of cond_resched(), depending on the kernel configuration. Hook into all of them. A more elegant solution might be to use a preempt notifier. However, non-ORC unwinders can't unwind a preempted task reliably. [1] https://lore.kernel.org/lkml/20220507174628.2086373-1-song@xxxxxxxxxx/ [2] https://lkml.kernel.org/lkml/20230120-vhost-klp-switching-v1-0-7c2b65519c43@xxxxxxxxxx Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> --- include/linux/livepatch.h | 1 + include/linux/livepatch_sched.h | 29 +++++++++++++++ include/linux/sched.h | 20 ++++++++--- kernel/livepatch/transition.c | 54 ++++++++++++++++++++++++++++ kernel/sched/core.c | 64 ++++++++++++++++++++++++++++----- 5 files changed, 155 insertions(+), 13 deletions(-) create mode 100644 include/linux/livepatch_sched.h diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h index 293e29960c6e..9b9b38e89563 100644 --- a/include/linux/livepatch.h +++ b/include/linux/livepatch.h @@ -13,6 +13,7 @@ #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 new file mode 100644 index 000000000000..013794fb5da0 --- /dev/null +++ b/include/linux/livepatch_sched.h @@ -0,0 +1,29 @@ +/* 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 4df2b3e76b30..2bc5e925a6d8 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -36,6 +36,7 @@ #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): */ @@ -2070,6 +2071,9 @@ 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) @@ -2078,6 +2082,7 @@ 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) @@ -2085,20 +2090,25 @@ static __always_inline int _cond_resched(void) return dynamic_cond_resched(); } -#else +#else /* !CONFIG_PREEMPTION */ static inline int _cond_resched(void) { + klp_sched_try_switch(); return __cond_resched(); } -#endif /* CONFIG_PREEMPT_DYNAMIC */ +#endif /* PREEMPT_DYNAMIC && CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */ -#else +#else /* CONFIG_PREEMPTION && !CONFIG_PREEMPT_DYNAMIC */ -static inline int _cond_resched(void) { return 0; } +static inline int _cond_resched(void) +{ + klp_sched_try_switch(); + return 0; +} -#endif /* !defined(CONFIG_PREEMPTION) || defined(CONFIG_PREEMPT_DYNAMIC) */ +#endif /* !CONFIG_PREEMPTION || CONFIG_PREEMPT_DYNAMIC */ #define cond_resched() ({ \ __might_resched(__FILE__, __LINE__, 0); \ diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c index 4d1f443778f7..e629966c6fbe 100644 --- a/kernel/livepatch/transition.c +++ b/kernel/livepatch/transition.c @@ -9,6 +9,7 @@ #include <linux/cpu.h> #include <linux/stacktrace.h> +#include <linux/static_call.h> #include "core.h" #include "patch.h" #include "transition.h" @@ -24,6 +25,25 @@ 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. @@ -76,6 +96,8 @@ static void klp_complete_transition(void) klp_transition_patch->mod->name, klp_target_state == KLP_PATCHED ? "patching" : "unpatching"); + klp_cond_resched_disable(); + if (klp_transition_patch->replace && klp_target_state == KLP_PATCHED) { klp_unpatch_replaced_patches(klp_transition_patch); klp_discard_nops(klp_transition_patch); @@ -338,6 +360,36 @@ 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; + + 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. @@ -496,6 +548,8 @@ void klp_start_transition(void) set_tsk_thread_flag(task, TIF_PATCH_PENDING); } + klp_cond_resched_enable(); + klp_signals_cnt = 0; } diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 3a0ef2fefbd5..ed5bf5ec0477 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -8500,6 +8500,7 @@ 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(); @@ -8648,13 +8649,17 @@ int sched_dynamic_mode(const char *str) #error "Unsupported PREEMPT_DYNAMIC mechanism" #endif -void sched_dynamic_update(int mode) +DEFINE_MUTEX(sched_dynamic_mutex); +static bool klp_override; + +static void __sched_dynamic_update(int mode) { /* * Avoid {NONE,VOLUNTARY} -> FULL transitions from ever ending up in * the ZERO state, which is invalid. */ - preempt_dynamic_enable(cond_resched); + if (!klp_override) + preempt_dynamic_enable(cond_resched); preempt_dynamic_enable(might_resched); preempt_dynamic_enable(preempt_schedule); preempt_dynamic_enable(preempt_schedule_notrace); @@ -8662,36 +8667,79 @@ void sched_dynamic_update(int mode) switch (mode) { case preempt_dynamic_none: - preempt_dynamic_enable(cond_resched); + if (!klp_override) + 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); - pr_info("Dynamic Preempt: none\n"); + if (mode != preempt_dynamic_mode) + pr_info("Dynamic Preempt: none\n"); break; case preempt_dynamic_voluntary: - preempt_dynamic_enable(cond_resched); + if (!klp_override) + 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); - pr_info("Dynamic Preempt: voluntary\n"); + if (mode != preempt_dynamic_mode) + pr_info("Dynamic Preempt: voluntary\n"); break; case preempt_dynamic_full: - preempt_dynamic_disable(cond_resched); + if (!klp_override) + 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); - pr_info("Dynamic Preempt: full\n"); + if (mode != preempt_dynamic_mode) + 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); -- 2.39.0
