[PATCH 3/4] x86/dumpstack: warn on stack recursion

[Josh Poimboeuf]

Print a warning if stack recursion is detected.

Use printk_deferred_once() because the unwinder can be called with the
console lock by lockdep via save_stack_trace().

Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 arch/x86/kernel/dumpstack_32.c | 5 ++++-
 arch/x86/kernel/dumpstack_64.c | 5 ++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/dumpstack_32.c b/arch/x86/kernel/dumpstack_32.c
index 90cf460..99ac8d2 100644
--- a/arch/x86/kernel/dumpstack_32.c
+++ b/arch/x86/kernel/dumpstack_32.c
@@ -109,8 +109,11 @@ int get_stack_info(unsigned long *stack, struct task_struct *task,
 	 * just break out and report an unknown stack type.
 	 */
 	if (visit_mask) {
-		if (*visit_mask & (1UL << info->type))
+		if (*visit_mask & (1UL << info->type)) {
+			printk_deferred_once(KERN_WARNING "WARNING: stack recursion on stack type %d\n",
+					     info->type);
 			goto unknown;
+		}
 		*visit_mask |= 1UL << info->type;
 	}
 
diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index 310abf4..26e6e83 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -128,8 +128,11 @@ int get_stack_info(unsigned long *stack, struct task_struct *task,
 	 * just break out and report an unknown stack type.
 	 */
 	if (visit_mask) {
-		if (*visit_mask & (1UL << info->type))
+		if (*visit_mask & (1UL << info->type)) {
+			printk_deferred_once(KERN_WARNING "WARNING: stack recursion on stack type %d\n",
+					     info->type);
 			goto unknown;
+		}
 		*visit_mask |= 1UL << info->type;
 	}
 
-- 
2.7.4