[PATCH 4/4] powerpc/cacheinfo: warn if cache object chain becomes unordered

[Nathan Lynch]

This can catch cases where the device tree has gotten mishandled into
an inconsistent state at runtime, e.g. the cache nodes for both the
source and the destination are present after a migration.

Signed-off-by: Nathan Lynch <nathanl at linux.ibm.com>
---
 arch/powerpc/kernel/cacheinfo.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/powerpc/kernel/cacheinfo.c b/arch/powerpc/kernel/cacheinfo.c
index 30be2cdc8aa9..5938aeeba8c0 100644
--- a/arch/powerpc/kernel/cacheinfo.c
+++ b/arch/powerpc/kernel/cacheinfo.c
@@ -425,6 +425,15 @@ static void link_cache_lists(struct cache *smaller, struct cache *bigger)
 	}
 
 	smaller->next_local = bigger;
+
+	/*
+	 * The cache->next_local list sorts by level ascending:
+	 * L1d -> L1i -> L2 -> L3 ...
+	 */
+	WARN_ONCE((smaller->level == 1 && bigger->level > 2) ||
+		  (smaller->level > 1 && bigger->level != smaller->level + 1),
+		  "linking L%i cache %pOFP to L%i cache %pOFP; skipped a level?\n",
+		  smaller->level, smaller->ofnode, bigger->level, bigger->ofnode);
 }
 
 static void do_subsidiary_caches_debugcheck(struct cache *cache)
-- 
2.20.1