Hi Petr
Thanks for review.
On 2026/9/1 23:04, Petr Pavlu wrote:
> On 8/31/26 9:21 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 overflow and populate failure paths of reserve_module_tags() now
>> release their reservation instead of leaking the maple tree entry.
>> 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().
>>
>> Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag
>> compression")
>> Reported-by: Sashiko <[email protected]>
>> Based-on-a-patch-by: Petr Pavlu <[email protected]>
>> Cc: Suren Baghdasaryan <[email protected]>
>> Signed-off-by: Hao Ge <[email protected]>
>> ---
>> Changes against Petr's prototype:
>> - allocate_codetag_sections() returns an error instead of void, and
>> only -EAGAIN falls back to a regular section. Any other error now
>> fails the load. The prototype fell back on everything, which can
>> leave live tags in module memory.
>> - reserve_module_tags() releases its reservation when populate fails
>> too, that path used to leak the maple tree entry.
>> - codetag_free_module_sections() on the move_module() error path uses
>> info->mod, the local mod is assigned only after a successful move.
>> - The percpu section is marked only when index.pcpu != 0, otherwise
>> sechdrs[0] gets marked.
>> - Dropped the SHF_ALLOC check, .codetag.* sections always have it.
>> ---
>> include/linux/module.h | 2 +
>> kernel/module/internal.h | 4 ++
>> kernel/module/main.c | 120 ++++++++++++++++++++-------------------
>> mm/alloc_tag.c | 9 ++-
>> 4 files changed, 75 insertions(+), 60 deletions(-)
>>
>> diff --git a/include/linux/module.h b/include/linux/module.h
>> index 7566815fabbe..33548daa31a3 100644
>> --- a/include/linux/module.h
>> +++ b/include/linux/module.h
>> @@ -325,6 +325,8 @@ enum mod_mem_type {
>> MOD_INIT_RODATA,
>>
>> MOD_MEM_NUM_TYPES,
>> +
>> + MOD_STANDALONE = -2,
>> MOD_INVALID = -1,
>> };
>>
>
> It might be better to split this patch into two: the first to introduce
> MOD_STANDALONE and use it only for the percpu section, and the second
> with all the codetag-related changes.
>
OK, will do for the next version.
> The introduction of SH_ENTSIZE_STANDALONE should also allow us to clean
> up the current resetting of SHF_ALLOC for the percpu section, and now
> also for codetag sections. The problem is that find_sec(".data..percpu")
I also like that this keeps SHF_ALLOC semantics closer to the ELF spec.
https://www.sco.com/developers/gabi/latest/ch4.sheader.html
SHF_ALLOC
The section occupies memory during process execution. Some control
sections do
not reside in the memory image of an object file; this attribute is off
for those sections.
(I spent some time reading up on this, so hopefully I've understood it
correctly.)
So it feels like we were taking a bit of a shortcut before.
These sections really do satisfy the SHF_ALLOC property by definition.
There were probably other reasons for doing it that way back then, but
either‑way
I think adding SH_ENTSIZE_STANDALONE is a much cleaner solution.
> can currently return different results depending on whether it is called
> before layout_and_allocate() or later. In addition, apply_relocations()
> needs a special case for SH_ENTSIZE_STANDALONE, where it could otherwise
> just test SHF_ALLOC.
>
Yeah, fair point.
> Instead of resetting SHF_ALLOC for percpu/codetag sections, both
> __layout_sections() and move_module() can check for
> SH_ENTSIZE_STANDALONE to determine whether a section is handled
> specially and should be skipped.
>
Right, While working on the code, I noticed that __layout_sections already has
a check for
this.
if ((s->sh_flags & masks[m][0]) != masks[m][0]
|| (s->sh_flags & masks[m][1])
|| s->sh_entsize != ~0UL
|| is_init != module_init_layout_section(sname))
continue;
s->sh_entsize != ~0UL can be used to handle this.
I'll add a short comment here.
> I think it would be useful to include this change in the first patch
> introducing MOD_STANDALONE, but I'm also ok with the current version.
> I can send a separate patch later to make more use of
> SH_ENTSIZE_STANDALONE in this way.
So cool.
>
>> @@ -2966,18 +2967,23 @@ static struct module *layout_and_allocate(struct
>> load_info *info, int flags)
>> */
>> module_mark_ro_after_init(info->hdr, info->sechdrs, info->secstrings);
>>
>> - /*
>> - * Determine total sizes, and put offsets in sh_entsize. For now
>> - * this is done generically; there doesn't appear to be any
>> - * special cases for the architectures.
>> - */
>> + /* Allow codetag sections to be allocated separately first. */
>> + err = allocate_codetag_sections(info);
>> + if (err) {
>> + codetag_free_module_sections(info->mod);
>
> The usual convention is that functions clean up after themselves on
> error. That means this codetag_free_module_sections() call should be
> done ideally by allocate_codetag_sections().
>
Ack.
Thanks
Best Regards
Hao
