[PATCH v6 13/18] perf: Skip user unwind if the task is a kernel thread.

From: Josh Poimboeuf <[email protected]>

If the task is not a user thread, there's no user stack to unwind.

Signed-off-by: Josh Poimboeuf <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>
---
Changes since v5: https://lore.kernel.org/[email protected]

- Use current->flags & PF_KTHREAD instead of current->mm == NULL.
  (Peter Zijlstra)

 kernel/events/core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 430dd158b1ee..ec9edf602974 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -8101,7 +8101,8 @@ struct perf_callchain_entry *
 perf_callchain(struct perf_event *event, struct pt_regs *regs)
 {
 	bool kernel = !event->attr.exclude_callchain_kernel;
-	bool user   = !event->attr.exclude_callchain_user;
+	bool user   = !event->attr.exclude_callchain_user &&
+		!(current->flags & PF_KTHREAD);
 	/* Disallow cross-task user callchains. */
 	bool crosstask = event->ctx->task && event->ctx->task != current;
 	const u32 max_stack = event->attr.sample_max_stack;
-- 
2.47.2