Re: [PATCH 3/4] maple_tree: Update internal warning and bug_on code

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

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@vger.kernel.org>
> Reported-by: Lorenzo Stoakes <ljs@kernel.org>
> 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@infradead.org>

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@kernel.org>

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