Re: [PATCH 3/4] maple_tree: Update internal warning and bug_on code
From: Lorenzo Stoakes (ARM)
Date: Wed Oct 28 2026 - 14:51:25 EST
ma
On Wed, Oct 28, 2026 at 11:42:17AM -0400, Liam R. Howlett (Google) wrote:
> When CONFIG_DEBUG_MAPLE_TREE is set, call the WARN_ON_ONCE() after the
> custom information is dumped about the tree. Without using the kernel's
> WARN_ON calls, syzbot will not catch issues detected by this code.
Mega nit but commit message doesn't mention the BUG_ON() bits :)
>
> Update the non-debug code to call WARN_ON_ONCE() as well.
>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Reported-by: Lorenzo Stoakes <ljs@xxxxxxxxxx>
> Fixes: bf857ddd21d0b ("maple_tree: move debug check to __mas_set_range()")
LLM overlord says bf857ddd21d0b only moved it, and f0a1f866aba1 actually
implemented it.
> Signed-off-by: Liam R. Howlett (Google) <liam@xxxxxxxxxxxxx>
Looks sensible to me from kernel perspective, but LLM overlord tells me this
changes the userland tests from asserting on dump_stack() to just printing
something out on WARN_ON().
(BUG_ON() is OK, it asserts already).
However we really do need this for the kernel so CONFIG_DEBUG_MAPLE_TREE
triggers syzbot and such, so maybe the userland bit can be a follow-up?
On that basis:
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>
Or... maybe just respin with something actually, can fix it by updating the
shared maple tree testing header to make warn do something like this
(schlopped, apologies):
diff --git a/tools/testing/shared/maple-shared.h b/tools/testing/shared/maple-shared.h
index 2a1e9a8594a2..112052e7201f 100644
--- a/tools/testing/shared/maple-shared.h
+++ b/tools/testing/shared/maple-shared.h
@@ -10,6 +10,30 @@
#include <time.h>
#include "linux/init.h"
+/*
+ * The tools/include/asm/bug.h WARN*() family only prints a message and
+ * carries on. Nothing in the maple tree or VMA tests expects a warning, so
+ * treat one as a failure and abort at the site.
+ */
+#undef WARN
+#undef WARN_ON
+#undef WARN_ON_ONCE
+#undef WARN_ONCE
+
+#define WARN(condition, format...) ({ \
+ int __ret_warn_on = !!(condition); \
+ if (unlikely(__ret_warn_on)) { \
+ fprintf(stderr, "WARN at %s:%d: ", __FILE__, __LINE__); \
+ fprintf(stderr, format); \
+ abort(); \
+ } \
+ unlikely(__ret_warn_on); \
+})
+
+#define WARN_ON(condition) WARN(condition, "%s\n", #condition)
+#define WARN_ON_ONCE(condition) WARN_ON(condition)
+#define WARN_ONCE(condition, format...) WARN(condition, format)
> ---
> include/linux/maple_tree.h | 54 +++++++++++++++++++++-----------------
> 1 file changed, 30 insertions(+), 24 deletions(-)
>
> diff --git a/include/linux/maple_tree.h b/include/linux/maple_tree.h
> index e30e57f5f3df9..0f96f1f19eb95 100644
> --- a/include/linux/maple_tree.h
> +++ b/include/linux/maple_tree.h
> @@ -680,7 +680,7 @@ void mt_cache_shrink(void);
> pr_info("Pass: %u Run:%u\n", \
> atomic_read(&maple_tree_tests_passed), \
> atomic_read(&maple_tree_tests_run)); \
> - dump_stack(); \
> + BUG_ON(1); \
> } else { \
> atomic_inc(&maple_tree_tests_passed); \
> } \
> @@ -696,7 +696,7 @@ void mt_cache_shrink(void);
> pr_info("Pass: %u Run:%u\n", \
> atomic_read(&maple_tree_tests_passed), \
> atomic_read(&maple_tree_tests_run)); \
> - dump_stack(); \
> + BUG_ON(1); \
> } else { \
> atomic_inc(&maple_tree_tests_passed); \
> } \
> @@ -713,62 +713,68 @@ void mt_cache_shrink(void);
> pr_info("Pass: %u Run:%u\n", \
> atomic_read(&maple_tree_tests_passed), \
> atomic_read(&maple_tree_tests_run)); \
> - dump_stack(); \
> + BUG_ON(1); \
> } else { \
> atomic_inc(&maple_tree_tests_passed); \
> } \
> } while (0)
>
> #define MT_WARN_ON(__tree, __x) ({ \
> + static bool __warned; \
> int ret = !!(__x); \
> atomic_inc(&maple_tree_tests_run); \
> - if (ret) { \
> - pr_info("WARN at %s:%d (%u)\n", \
> - __func__, __LINE__, __x); \
> + if (!ret) { \
> + atomic_inc(&maple_tree_tests_passed); \
> + } else if (!__warned) { \
> + __warned = true; \
> + pr_info("WARN at %s:%d\n", \
> + __func__, __LINE__); \
> mt_dump(__tree, mt_dump_hex); \
> pr_info("Pass: %u Run:%u\n", \
> atomic_read(&maple_tree_tests_passed), \
> atomic_read(&maple_tree_tests_run)); \
> - dump_stack(); \
> - } else { \
> - atomic_inc(&maple_tree_tests_passed); \
> + WARN_ON(1); \
> } \
> unlikely(ret); \
> })
>
> #define MAS_WARN_ON(__mas, __x) ({ \
> + static bool __warned; \
> int ret = !!(__x); \
> atomic_inc(&maple_tree_tests_run); \
> - if (ret) { \
> - pr_info("WARN at %s:%d (%u)\n", \
> - __func__, __LINE__, __x); \
> + if (!ret) { \
> + atomic_inc(&maple_tree_tests_passed); \
> + } else if (!__warned) { \
> + __warned = true; \
> + pr_info("WARN at %s:%d\n", \
> + __func__, __LINE__); \
> mas_dump(__mas); \
> mt_dump((__mas)->tree, mt_dump_hex); \
> pr_info("Pass: %u Run:%u\n", \
> atomic_read(&maple_tree_tests_passed), \
> atomic_read(&maple_tree_tests_run)); \
> - dump_stack(); \
> - } else { \
> - atomic_inc(&maple_tree_tests_passed); \
> + WARN_ON(1); \
> } \
> unlikely(ret); \
> })
>
> #define MAS_WR_WARN_ON(__wrmas, __x) ({ \
> + static bool __warned; \
> int ret = !!(__x); \
> atomic_inc(&maple_tree_tests_run); \
> - if (ret) { \
> - pr_info("WARN at %s:%d (%u)\n", \
> - __func__, __LINE__, __x); \
> + if (!ret) { \
> + atomic_inc(&maple_tree_tests_passed); \
> + } else if (!__warned) { \
> + __warned = true; \
> + pr_info("WARN at %s:%d\n", \
> + __func__, __LINE__); \
> mas_wr_dump(__wrmas); \
> mas_dump((__wrmas)->mas); \
> mt_dump((__wrmas)->mas->tree, mt_dump_hex); \
> pr_info("Pass: %u Run:%u\n", \
> atomic_read(&maple_tree_tests_passed), \
> atomic_read(&maple_tree_tests_run)); \
> - dump_stack(); \
> - } else { \
> - atomic_inc(&maple_tree_tests_passed); \
> + WARN_ON(1); \
> } \
> unlikely(ret); \
> })
> @@ -776,9 +782,9 @@ void mt_cache_shrink(void);
> #define MT_BUG_ON(__tree, __x) BUG_ON(__x)
> #define MAS_BUG_ON(__mas, __x) BUG_ON(__x)
> #define MAS_WR_BUG_ON(__mas, __x) BUG_ON(__x)
> -#define MT_WARN_ON(__tree, __x) WARN_ON(__x)
> -#define MAS_WARN_ON(__mas, __x) WARN_ON(__x)
> -#define MAS_WR_WARN_ON(__mas, __x) WARN_ON(__x)
> +#define MT_WARN_ON(__tree, __x) WARN_ON_ONCE(__x)
> +#define MAS_WARN_ON(__mas, __x) WARN_ON_ONCE(__x)
> +#define MAS_WR_WARN_ON(__mas, __x) WARN_ON_ONCE(__x)
> #endif /* CONFIG_DEBUG_MAPLE_TREE */
>
> /**
> --
> 2.47.3
>
--
Cheers, Lorenzo