Re: [PATCH v11 0/7] alloc_tag and module codetag section fixes

[Uladzislau Rezki <urezki@gmail.com>]

On Wed, Sep 30, 2026 at 11:26:41AM +0800, Hao Ge wrote:
> Hi Suren and Andrew
> 
> 
> On 2026/9/30 10:39, Suren Baghdasaryan wrote:
> > On Tue, Sep 29, 2026 at 8:44 PM Andrew Morton <akpm@linux-foundation.org> wrote:
> >>
> >> On Tue, 29 Sep 2026 16:20:07 +0800 Hao Ge <hao.ge@linux.dev> wrote:
> >>
> >>> With profiling toggled off, the overflow check in
> >>> reserve_module_tags() 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. On overflow the fix shuts
> >>> profiling down, releases the reservation and returns -EAGAIN, and
> >>> the codetag section lands as regular module data in the same load,
> >>> so the module loads without profiling.
> >>>
> >>> Review of the earlier series by Sashiko turned up more problems.
> >>>
> >>> One is a race. layout_sections() and move_module() both asked
> >>> codetag_needs_module_section() where a codetag section goes, and
> >>> mem_profiling_support can change between the two calls, for instance
> >>> when another module load overflows the tag index and shuts profiling
> >>> down. move_module() then copied the codetag section to offset 0 of
> >>> its regular destination and clobbered the first section placed in
> >>> that region.
> >>>
> >>> v7 reworks where codetag sections are allocated, on a prototype by
> >>> Petr Pavlu [1]. The allocation runs before layout_sections() and the
> >>> placement is decided in one step, so nothing re-asks the question
> >>> and the race is gone. The retry is gone too, on -EAGAIN the section
> >>> is laid out as regular module data right in the same load.
> >>
> >> Thanks.
> >>
> >> Seven patches, all cc:stable.  Why is a backport proposed?
> >> Documentation/process/stable-kernel-rules.rst gives guidelines - does
> >> this series meet them?  Does Suren have thoughts?
> 
> Thanks, I've just gone through this carefully.
> 
> > 
> > I think vmalloc fix in patch#2 should be posted separately and clearly
> > quialifies for backporting as if fixes issues Hao found at [1].
> 
> Agreed. Patch #2 was added to this patch series because vm_module_tags_populate
> suffers from the same issue. If we want to be more conservative, I'd prefer to keep
> vm_module_tags_populate as it was in V10:
> https://lore.kernel.org/all/20260915070001.113559-3-hao.ge@linux.dev/
> 
> Then we can submit a fix for __GFP_NOFAIL retry loop in __vmalloc_area_node() as a hotfix together
> with our new patch #2. While at it, we can also check if there are any unnecessary calls to
> vunmap_range family functions that can be cleaned up now that patch #2 is applied.
> 
Yep, this should be a separate fix for vmalloc.

--
Uladzislau Rezki