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

[Liam R. Howlett (Google)]

On 26/10/28 05:54PM, Lorenzo Stoakes (ARM) wrote:
> 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?

Wow, so any WARN() before... I'm trying not to think about it.

The change below is good to be squashed into the fix I sent.  It also
makes vma warnings fatal - which should also happen.

Andrew, can you take care of this or would you rather a respin?


> 
> 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