[PATCH 3/4] maple_tree: Update internal warning and bug_on code
Liam R. Howlett (Google)
liam at infradead.org
Wed Oct 28 11:37:41 PDT 2026
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 at vger.kernel.org>
> > Reported-by: Lorenzo Stoakes <ljs at 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 at 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?
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 at 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
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