[PATCH] of: unittest: Remove refcount underflow tests

[Danilo Krummrich <dakr@kernel.org>]

With CONFIG_OF_UNITTEST=y and CONFIG_BUG_ON_DATA_CORRUPTION=y, the
machine no longer boots after commit 5b5224220747 ("refcount: Use
CONFIG_BUG_ON_DATA_CORRUPTION for UAF-related errors").

of_unittest_lifecycle() deliberately calls of_node_put() after the
node's reference count has reached zero. The test expects a warning and
continues to check that a subsequent put does not produce another
warning. With BUG_ON_DATA_CORRUPTION enabled, refcount underflow now
triggers BUG() instead. This panics the kernel during boot:

	kernel BUG at lib/refcount.c:37!
	Oops: invalid opcode: 0000 [#1] SMP NOPTI
	CPU: 1 UID: 0 PID: 1 Comm: swapper/0 Tainted: G                 N  7.3.0+ #14 PREEMPT(full)
	RIP: 0010:refcount_warn_saturate+0x89/0x90
	Call Trace:
	 of_unittest_lifecycle+0x158/0x310
	 of_unittest+0x105/0x130
	 do_one_initcall+0x127/0x350
	 do_initcall_level+0x7c/0xe0
	 do_initcalls+0x59/0xa0
	 kernel_init_freeable+0x118/0x1a0
	 kernel_init+0x1f/0x140
	Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b

Remove the refcount underflow tests, which exercise the refcount
implementation rather than OF-specific behavior.

Fixes: 5b5224220747 ("refcount: Use CONFIG_BUG_ON_DATA_CORRUPTION for UAF-related errors")
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 drivers/of/unittest.c | 43 -------------------------------------------
 1 file changed, 43 deletions(-)

diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
index e255f54f4d76..03fc941c0995 100644
--- a/drivers/of/unittest.c
+++ b/drivers/of/unittest.c
@@ -3678,9 +3678,6 @@ static void __init of_unittest_lifecycle(void)
 	 * - Decrementing refcount to zero via of_node_put() should cause the
 	 *   attempt to free the node memory by of_node_release() to fail
 	 *   because the node is not a dynamic node.
-	 *
-	 * - Decrementing refcount past zero should result in additional
-	 *   errors reported.
 	 */
 
 	np = of_find_node_by_path(refcount_path);
@@ -3714,46 +3711,6 @@ static void __init of_unittest_lifecycle(void)
 
 	EXPECT_END(KERN_INFO, "OF: ERROR: of_node_release() detected bad of_node_put() on /testcase-data/refcount-node");
 
-
-	/*
-	 * expect stack trace for subsequent of_node_put():
-	 *   __refcount_sub_and_test() calls:
-	 *   refcount_warn_saturate(r, REFCOUNT_SUB_UAF)
-	 *
-	 * Not capturing entire WARN_ONCE() trace with EXPECT_*(), just
-	 * the first three lines, and the last line.
-	 */
-	EXPECT_BEGIN(KERN_INFO, "------------[ cut here ]------------");
-	EXPECT_BEGIN(KERN_INFO, "WARNING: <<all>>");
-	EXPECT_BEGIN(KERN_INFO, "refcount_t: underflow; use-after-free.");
-	EXPECT_BEGIN(KERN_INFO, "---[ end trace <<int>> ]---");
-
-	/* refcount is now zero, this should fail */
-	unittest(1, "/testcase-data/refcount-node is zero");
-	of_node_put(np);
-
-	EXPECT_END(KERN_INFO, "---[ end trace <<int>> ]---");
-	EXPECT_END(KERN_INFO, "refcount_t: underflow; use-after-free.");
-	EXPECT_END(KERN_INFO, "WARNING: <<all>>");
-	EXPECT_END(KERN_INFO, "------------[ cut here ]------------");
-
-	/*
-	 * Q. do we expect to get yet another warning?
-	 * A. no, the WARNING is from WARN_ONCE()
-	 */
-	EXPECT_NOT_BEGIN(KERN_INFO, "------------[ cut here ]------------");
-	EXPECT_NOT_BEGIN(KERN_INFO, "WARNING: <<all>>");
-	EXPECT_NOT_BEGIN(KERN_INFO, "refcount_t: underflow; use-after-free.");
-	EXPECT_NOT_BEGIN(KERN_INFO, "---[ end trace <<int>> ]---");
-
-	unittest(1, "/testcase-data/refcount-node is zero, second time");
-	of_node_put(np);
-
-	EXPECT_NOT_END(KERN_INFO, "---[ end trace <<int>> ]---");
-	EXPECT_NOT_END(KERN_INFO, "refcount_t: underflow; use-after-free.");
-	EXPECT_NOT_END(KERN_INFO, "WARNING: <<all>>");
-	EXPECT_NOT_END(KERN_INFO, "------------[ cut here ]------------");
-
 	/*
 	 * refcount of zero will trigger stack traces from any further
 	 * attempt to of_node_get() node "refcount-node". One example of

base-commit: a287f97d4256b5f5527f5b5a54f8ada55e1482c7
-- 
2.56.0