[PATCH v4] sched/debug: Dump end of stack when detected corrupted

[Feng Tang]

When debugging a kernel hang during suspend/resume [1], there were random
memory corruptions in different places like ACPI, file systems, network
subsystems, and reported by slub_debug+KASAN or detected by scheduler with
error message:

  "Kernel panic - not syncing: corrupted stack end detected inside scheduler"

So dump the corrupted memory around the stack end to give more direct
hints about how the memory is corrupted:

 "
 Corrupted Stack: ff11000122770000: ff ff ff ff ff ff 14 91 82 3b 78 e8 08 00 45 00  .........;x...E.
 Corrupted Stack: ff11000122770010: 00 1d 2a ff 40 00 40 11 98 c8 0a ef 30 2c 0a ef  ..*.@.@.....0,..
 Corrupted Stack: ff11000122770020: 30 ff a2 00 22 3d 00 09 9a 95 2a 00 00 00 00 00  0..."=....*.....
 ...
 Kernel panic - not syncing: corrupted stack end detected inside scheduler
 "

And with it, the culprit was quickly identified to be ethernet driver
that it frees RX related memory back to kernel in suspend hook, but
its HW is not really stopped, and still send RX data to those old
buffer through DMA.

The intention is trying to find a common pattern by comparing the dumped
memory of many different reproduced samples, for those hard-to-track
random memory corruption cases.

[1]. https://bugzilla.kernel.org/show_bug.cgi?id=217854

Signed-off-by: Feng Tang <feng.tang@xxxxxxxxxxxxxxxxx>
Reviewed-by: John Paul Adrian Glaubitz <glaubitz@xxxxxxxxxxxxxxxxxxx>
---
Changlog:

  since v3:
      * Refine commit log and rebase to latest kernel 
      * Update email address

  since v2:
      * Change code format (Adrian)
      * Add Reviewed tag from Adrian
      
  since v1:
      * Refine the commit log with more info, and rebase againt 6.8-rc3

 kernel/sched/core.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 87540217fc09..a894d402e576 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5929,8 +5929,19 @@ static noinline void __schedule_bug(struct task_struct *prev)
 static inline void schedule_debug(struct task_struct *prev, bool preempt)
 {
 #ifdef CONFIG_SCHED_STACK_END_CHECK
-	if (task_stack_end_corrupted(prev))
+	if (task_stack_end_corrupted(prev)) {
+		unsigned long *ptr = end_of_stack(prev);
+
+		/* Dump 16 ulong words around the corruption point */
+#ifdef CONFIG_STACK_GROWSUP
+		ptr -= 15;
+#endif
+		print_hex_dump(KERN_ERR, "Corrupted Stack: ",
+			DUMP_PREFIX_ADDRESS, 16, 1, ptr,
+			16 * sizeof(unsigned long), true);
+
 		panic("corrupted stack end detected inside scheduler\n");
+	}
 
 	if (task_scs_end_corrupted(prev))
 		panic("corrupted shadow stack detected inside scheduler\n");
-- 
2.39.5 (Apple Git-154)