[PATCH] alloc_tag: fix undetected compressed tag overflow when profiling is disabled

[Hao Ge <hao.ge@linux.dev>]

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.

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.

Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression")
Cc: stable@vger.kernel.org
Signed-off-by: Hao Ge <hao.ge@linux.dev>
---
 mm/alloc_tag.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c
index 52aece27b00e..a387a17211de 100644
--- a/mm/alloc_tag.c
+++ b/mm/alloc_tag.c
@@ -904,7 +904,7 @@ static void *reserve_module_tags(struct module *mod, unsigned long size,
 		int grow_res;
 
 		module_tags.size = offset + size;
-		if (mem_alloc_profiling_enabled() && !tags_addressable()) {
+		if (!tags_addressable()) {
 			shutdown_mem_profiling(true);
 			pr_warn("With module %s there are too many tags to fit in %d page flag bits. Memory allocation profiling is disabled!\n",
 				mod->name, NR_UNUSED_PAGEFLAG_BITS);
-- 
2.25.1