There are a few places in the kernel that access stack memory
belonging to a different task. Before we can start freeing task
stacks before the task_struct is freed, we need a way for those code
paths to pin the stack.
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
---
include/linux/sched.h | 16 ++++++++++++++++
init/Kconfig | 3 +++
2 files changed, 19 insertions(+)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4108b4880b86..18bef18fef88 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -3063,11 +3063,19 @@ static inline struct thread_info *task_thread_info(struct task_struct *task)
{
return &task->thread_info;
}
+
+/*
+ * When accessing the stack of a non-current task that might exit, use
+ * try_get_task_stack() instead. task_stack_page will return a pointer
+ * that could get freed out from under you.
+ */
static inline void *task_stack_page(const struct task_struct *task)
{
return task->stack;
}
+
#define setup_thread_stack(new,old) do { } while(0)
+
static inline unsigned long *end_of_stack(const struct task_struct *task)
{
return task->stack;
@@ -3103,6 +3111,14 @@ static inline unsigned long *end_of_stack(struct task_struct *p)
}
#endif
+
+static inline void *try_get_task_stack(struct task_struct *tsk)
+{
+ return task_stack_page(tsk);
+}
+
+static inline void put_task_stack(struct task_struct *tsk) {}
+
#define task_stack_end_corrupted(task) \
(*(end_of_stack(task)) != STACK_END_MAGIC)
diff --git a/init/Kconfig b/init/Kconfig
index 2cdf20e03b1f..8823df60d312 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -33,6 +33,9 @@ config THREAD_INFO_IN_TASK
make this work, an arch will need to remove all thread_info fields
except flags and fix any runtime bugs.
+ One subtle change that will be needed is to use try_get_task_stack()
+ and put_task_stack() in save_thread_stack_tsk().
+
menu "General setup"
config BROKEN
--
2.7.4
--
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