* Re: [PATCH] alloc_tag: fix undetected compressed tag overflow when profiling is disabled
[not found] <20260804064408.105033-1-hao.ge@linux.dev>
@ 2026-08-04 23:42 ` Andrew Morton
0 siblings, 0 replies; only message in thread
From: Andrew Morton @ 2026-08-04 23:42 UTC (permalink / raw)
To: Hao Ge; +Cc: Suren Baghdasaryan, linux-mm, linux-kernel, Abhishek Bapat,
stable
On Tue, 4 Aug 2026 14:44:08 +0800 Hao Ge <hao.ge@linux.dev> wrote:
> In reserve_module_tags(), the tag overflow check is gated on
> mem_alloc_profiling_enabled():
>
> if (mem_alloc_profiling_enabled() && !tags_addressable())
>
> If profiling is toggled off at runtime and a module is loaded whose
> tags exceed the compressed-mode limit, shutdown_mem_profiling() is
> skipped. vm_module_tags_populate() still maps memory for the tags and
> the module loads successfully, but the total tag count now exceeds what
> NR_UNUSED_PAGEFLAG_BITS can address.
>
> Once profiling is re-enabled, ref_to_idx() computes each tag's index
> as its position in the alloc_tag array. update_page_tag_ref() masks
> it to alloc_tag_ref_mask before storing in page->flags. Indices
> beyond the mask are truncated and idx_to_ref() resolves them to wrong
> tags.
With bad effects, one assumes.
When fixing a bug please always include a complete description of the
userspace-visible runtime effects of that bug.
> mem_alloc_profiling_enabled() and mem_profiling_compressed are
> independent. Once compressed mode is established at boot, it stays
> active regardless of runtime toggles of mem_profiling.
>
> We therefore remove the mem_alloc_profiling_enabled() guard.
It appears that AI review has found a pre-existing error-path cleanup
issue:
https://sashiko.dev/#/patchset/20260804064408.105033-1-hao.ge@linux.dev
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