Re: [PATCH v2 0/2] mm/cma: fix range selection in cma_declare_contiguous_multi()

[Mike Rapoport]

On Wed, Oct 14, 2026 at 08:53:39PM -0600, Ivy Lopez wrote:
> These two patches fix two independent bugs in the multi-range selection
> of cma_declare_contiguous_multi(), found by code inspection with the
> help of an LLM (both patches carry Assisted-by: LLM).

cma_declare_contiguous_multi() seems broken in many ways.
I'm working on a patch to rewrite it.
 
> Patch 1 fixes list_insert_sorted(), which does not actually sort: it
> stops at the wrong entry and, when no entry matches, inserts before the
> last entry instead of appending. The caller assumes the list tail is the
> smallest recorded range and that the list is walked largest first.
> 
> Patch 2 fixes sizesum counting the size of ranges that were skipped
> because the list was full, so the sizesum < total_size check can pass
> when the recorded ranges cannot cover the request, and the function
> returns 0 having reserved less than asked for.
> 
> Each patch fixes a distinct failure and neither depends on the other.
> No kernel-level reproducer was produced and nothing was tested beyond
> compiling; the examples in the commit messages come from a userspace
> copy of the helper and the selection loop, written from the source.
> 
> Changes in v2:
> - resend as a series with a cover letter, as requested by Lorenzo
> - commit messages now state how the bugs were found and that they were
>   not tested on hardware or in a booted kernel
> - add Assisted-by: LLM
> - patch 1: correct the sentence about the first inserted range staying
>   at the tail (only until it is evicted)
> - rebased on the current akpm/mm-new
> - no code changes
> 
> v1: https://lore.kernel.org/all/20261011003059.169430-1-skunkolee@xxxxxxxxx/
> 
> Ivy Lopez (2):
>   mm/cma: fix list_insert_sorted() ordering
>   mm/cma: do not count skipped ranges in cma_declare_contiguous_multi()
> 
>  mm/cma.c | 16 ++++++----------
>  1 file changed, 6 insertions(+), 10 deletions(-)
> 
> -- 
> 2.56.0
> 
> 

-- 
Sincerely yours,
Mike.