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. This silently corrupts /proc/allocinfo: allocated pages get attributed to the wrong call sites, so the statistics it reports are wrong. 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. Remove the mem_alloc_profiling_enabled() guard. Also return an error after shutdown_mem_profiling() to skip vm_module_tags_populate(), as the mapped pages would never be reused - shutdown_mem_profiling() sets mem_profiling_support to false, so no future module load enters the codetag path. Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression") Cc: stable@vger.kernel.org Signed-off-by: Hao Ge --- Changes in v3: - use pr_warn_once() instead of pr_warn() - return -ENOMEM instead of -ENOSPC (Suren) - expand the commit message to describe the /proc/allocinfo impact (Andrew) Changes in v2: - return an error after shutdown_mem_profiling() to skip vm_module_tags_populate() v1: https://lore.kernel.org/all/20260804064408.105033-1-hao.ge@linux.dev/ v2: https://lore.kernel.org/all/20260804122038.190270-1-hao.ge@linux.dev/ --- mm/alloc_tag.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c index 52aece27b00e..35ef2bbfa13a 100644 --- a/mm/alloc_tag.c +++ b/mm/alloc_tag.c @@ -904,10 +904,11 @@ 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); + pr_warn_once("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); + return ERR_PTR(-ENOMEM); } grow_res = vm_module_tags_populate(); -- 2.25.1