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

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

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.

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.

Tested on an x86_64 virtual machine:

# insmod overflow_tag.ko
# dmesg
  With module overflow_tag there are too many tags to fit in 13 page
  flag bits. Memory allocation profiling is disabled!
# rmmod overflow_tag
The module loads without profiling.

Changes in v4:
- add a new patch (1/2) to move release_module_tags() above
  reserve_module_tags(); the overflow fix is 2/2
- release the reservation on the -EAGAIN path
- return -EAGAIN instead of -ENOMEM so the module can still load
  without profiling (Suren)
- reset sh_addr, mem[type].size and sym/str SHF_ALLOC before retry
- skip percpu counters in load_module() when profiling is off

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/
v3: https://lore.kernel.org/all/20260805090633.141001-1-hao.ge@linux.dev/

Hao Ge (2):
  alloc_tag: move release_module_tags() above reserve_module_tags()
  alloc_tag: fix undetected compressed tag overflow when profiling is
    disabled

 kernel/module/main.c |  17 ++++++++-
 mm/alloc_tag.c       | 103 +++++++++++++++++++++++++++------------------------
 2 files changed, 69 insertions(+), 51 deletions(-)

-- 
2.25.1