Re: [PATCH] mm: nommu: add sysctl_max_map_count() check for do_mmap()

[Andrew Morton]

On Thu,  2 Jul 2026 10:28:30 +0900 Hajime Tazaki <thehajime@xxxxxxxxx> wrote:

> The sysctl variable vm.max_map_count (sysctl_max_map_count) is not
> expose under !MMU case but used it wit the default vaule
> DEFAULT_MAX_MAP_COUNT as a limit of count.  This is currently used when
> a vma entry is split into two chunks (split_vma()) but not used when
> allocated (do_mmap()).  As a result, even if users request a large
> number of allocate memory, it will keep allocating until OOM happens.
> 
> This commit introduces a check at the begining of do_mmap in nommu.c to
> prevent this situation.
> 
> This is detected with a LTP (Linux Test Project) test, which linked
> below.

AI review flagged a couple of issues in the current code, one quite
serious:

https://sashiko.dev/#/patchset/20260702012830.667205-1-thehajime@xxxxxxxxx