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

[Petr Pavlu]

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@xxxxxxxxxx>
> Link: https://lore.kernel.org/all/499bb60c-c6e3-43a3-bd92-95a0567ece5e@xxxxxxxx/ [1]
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Hao Ge <hao.ge@xxxxxxxxx>

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

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

-- 
Thanks,
Petr