[PATCH] stacktrace: check whether task has a stack before saving it

[Ronald Wahl]

I encountered a crash on ARM32 when trying to dump the stack of some
zombie process. This is caused by a missing check whether the task
actually has a valid stack. This commit adds this check.

Commit 214d8ca6ee85 ("stacktrace: Provide common infrastructure")
introduced this check for platforms that define CONFIG_ARCH_STACKWALK
but ARM32 is not one of them.

Signed-off-by: Ronald Wahl <ronald.wahl@xxxxxxxxxxx>
---
 kernel/stacktrace.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
index 9ed5ce989415..38ae52349306 100644
--- a/kernel/stacktrace.c
+++ b/kernel/stacktrace.c
@@ -298,6 +298,9 @@ unsigned int stack_trace_save_tsk(struct task_struct *task,
 		.skip	= skipnr + (current == task),
 	};

+	if (!try_get_task_stack(task))
+		return 0;
+
 	save_stack_trace_tsk(task, &trace);
 	return trace.nr_entries;
 }
--
2.41.0