[RFC] sched,livepatch: call klp_try_switch_task in __cond_resched

[Song Liu]

Busy kernel threads may block the transition of livepatch. Call
klp_try_switch_task from __cond_resched to make the transition easier.

Signed-off-by: Song Liu <song@xxxxxxxxxx>
---
 include/linux/livepatch.h     | 2 ++
 kernel/livepatch/transition.c | 2 +-
 kernel/sched/core.c           | 3 +++
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 2614247a9781..a9209f62550a 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -236,6 +236,7 @@ int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
 			     unsigned int symindex, unsigned int secindex,
 			     const char *objname);
 
+bool klp_try_switch_task(struct task_struct *task);
 #else /* !CONFIG_LIVEPATCH */
 
 static inline int klp_module_coming(struct module *mod) { return 0; }
@@ -253,6 +254,7 @@ int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
 	return 0;
 }
 
+bool klp_try_switch_task(struct task_struct *task) { return true; }
 #endif /* CONFIG_LIVEPATCH */
 
 #endif /* _LINUX_LIVEPATCH_H_ */
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index f6310f848f34..4257a8eec64b 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -278,7 +278,7 @@ static int klp_check_stack(struct task_struct *task, char *err_buf)
  * running, or it's sleeping on a to-be-patched or to-be-unpatched function, or
  * if the stack is unreliable, return false.
  */
-static bool klp_try_switch_task(struct task_struct *task)
+bool klp_try_switch_task(struct task_struct *task)
 {
 	static char err_buf[STACK_ERR_BUF_SIZE];
 	struct rq *rq;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a7302b7b65f2..41d1c7a86912 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6990,6 +6990,9 @@ SYSCALL_DEFINE0(sched_yield)
 #if !defined(CONFIG_PREEMPTION) || defined(CONFIG_PREEMPT_DYNAMIC)
 int __sched __cond_resched(void)
 {
+	if (unlikely(klp_patch_pending(current)))
+		klp_try_switch_task(current);
+
 	if (should_resched(0)) {
 		preempt_schedule_common();
 		return 1;
-- 
2.30.2