Re: [PATCH v4 0/2] alloc_tag: fix undetected compressed tag overflow when profiling is disabled

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 10 Aug 2026 17:39:53 +0800 Hao Ge <hao.ge@linux.dev> wrote:

> v3 was a single patch. After discussion with Suren and Andrew we went
> for a more graceful approach: rather than failing the module load on
> overflow, let it load without profiling. Once profiling is disabled,
> codetag_needs_module_section() returns false, so on retry the codetag
> section is placed as regular module data.
> 
> A new patch (1/2) is added to move release_module_tags() above
> reserve_module_tags(), since the overflow path now has to call it and
> the helper sits below it.

Thing is, [2/2] has cc:stable but it requires [1/2] to be able to be
compiled.  [1/2] doesn't have cc:stable so we're asking -stable folks
to backport a patch which doesn't compile.

Resolve this by using the same Fixes: and cc:stable in both patches.

> release_module_tags() is what module unload calls to drop a module's
> reservation from the maple tree. By the time reserve_module_tags()
> detects the overflow it has already stored that reservation, and the
> -EAGAIN return skips vm_module_tags_populate(), so the backing pages
> never get mapped. If reserve_module_tags() returns without calling
> release_module_tags(), the stale entry keeps pointing at that unmapped
> range; when the module is later unloaded, release_module_tags() walks
> it and panics.

AI review had a lot to say about this patchset.  Some pre-existing, some
not:
	https://sashiko.dev/#/patchset/20260810093955.153015-1-hao.ge@linux.dev



offtopic: alloc_tag isn't getting allmodconfig build coverage at this
time because:

1: MEM_ALLOC_PROFILING depends on !DEBUG_FORCE_WEAK_PER_CPU (why?  I
   can't figure that out)

2: x86_64 allmodconfig enables DEBUG_FORCE_WEAK_PER_CPU, despite it
   being for s390 and alpha.  In fact it might be alpha-only.

Adding

	depends on ALPHA || S390

in there fixes this.