Re: [PATCH v9 4/4] module: allocate codetag sections before the regular module layout

On 9/8/26 11:24 AM, Hao Ge wrote:

Whether a codetag section goes to the codetag region is decided by
layout_sections() and asked again in move_module(). A concurrent
load can shut profiling down in between, and move_module() then
copies the section to offset 0 of its regular destination,
overwriting whatever is there.

Decide and allocate in one pass, before the layout. Allocation
errors fail the load. On a tag area overflow profiling is already
disabled, so -EAGAIN makes the section fall back to regular module
data and the module still loads. The reservation is released and
module_tags.size rolled back, so a concurrent load which already
passed needs_section_mem() does not skip vm_module_tags_populate()

An SHT_NOBITS codetag section is zeroed explicitly, the tag area
pages are not zeroed on allocation.

When profiling was toggled off the overflow check did not run, a
module could load with more tags than the page flags can address,
and re-enabling profiling then silently corrupted /proc/allocinfo.
The check no longer depends on mem_alloc_profiling_enabled().

Based on a patch by Petr Pavlu [1].

Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Link: https://lore.kernel.org/all/499bb60c-c6e3-43a3-bd92-95a0567ece5e@suse.com/ (local) [1]
Cc: stable@vger.kernel.org
Signed-off-by: Hao Ge <hao.ge@linux.dev>

This looks ok to me from the module loader's perspective.

Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>

-- 
Thanks,
Petr