[RESEND][PATCH v15 1/4] unwind deferred: Add unwind_user_get_cookie() API

[Steven Rostedt <rostedt@kernel.org>]

From: Steven Rostedt <rostedt@goodmis.org>

Add the function unwind_user_get_cookie() API that allows a subsystem to
retrieve the current context cookie. This can be used by perf to attach a
cookie to its task deferred unwinding code that doesn't use the deferred
unwind logic.

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 include/linux/unwind_deferred.h |  5 +++++
 kernel/unwind/deferred.c        | 21 +++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/include/linux/unwind_deferred.h b/include/linux/unwind_deferred.h
index 26122d00708a..ce507495972c 100644
--- a/include/linux/unwind_deferred.h
+++ b/include/linux/unwind_deferred.h
@@ -41,6 +41,8 @@ void unwind_deferred_cancel(struct unwind_work *work);
 
 void unwind_deferred_task_exit(struct task_struct *task);
 
+u64 unwind_user_get_cookie(void);
+
 static __always_inline void unwind_reset_info(void)
 {
 	struct unwind_task_info *info = &current->unwind_info;
@@ -76,6 +78,9 @@ static inline void unwind_deferred_cancel(struct unwind_work *work) {}
 static inline void unwind_deferred_task_exit(struct task_struct *task) {}
 static inline void unwind_reset_info(void) {}
 
+/* Must be non-zero */
+static inline u64 unwind_user_get_cookie(void) { return (u64)-1; }
+
 #endif /* !CONFIG_UNWIND_USER */
 
 #endif /* _LINUX_UNWIND_USER_DEFERRED_H */
diff --git a/kernel/unwind/deferred.c b/kernel/unwind/deferred.c
index dc6040aae3ee..90f90e30000a 100644
--- a/kernel/unwind/deferred.c
+++ b/kernel/unwind/deferred.c
@@ -94,6 +94,27 @@ static u64 get_cookie(struct unwind_task_info *info)
 	return info->id.id;
 }
 
+/**
+ * unwind_user_get_cookie - Get the current user context cookie
+ *
+ * This is used to get a unique context cookie for the current task.
+ * Every time a task enters the kernel it has a new context. If
+ * a subsystem needs to have a unique identifier for that context for
+ * the current task, it can call this function to retrieve a unique
+ * cookie for that task context.
+ *
+ * Returns: A unque identifier for the current task user context.
+ */
+u64 unwind_user_get_cookie(void)
+{
+	struct unwind_task_info *info = &current->unwind_info;
+
+	guard(irqsave)();
+	/* Make sure to clear the info->id.id when exiting the kernel */
+	set_bit(UNWIND_USED_BIT, &info->unwind_mask);
+	return get_cookie(info);
+}
+
 /**
  * unwind_user_faultable - Produce a user stacktrace in faultable context
  * @trace: The descriptor that will store the user stacktrace
-- 
2.50.1