Hi Suren、David、Lorenzo On 2026/9/17 09:12, Hao Ge wrote: > Hi Suren > > On 2026/9/17 03:07, Suren Baghdasaryan wrote: >> On Wed, Sep 16, 2026 at 9:31 AM Suren Baghdasaryan <[email protected]> wrote: >>> >>> On Tue, Sep 15, 2026 at 11:00 PM Hao Ge <[email protected]> wrote: >>>> >>>> Hi Suren >>>> >>>> Thanks for you review. >>>> >>>> On 2026/9/16 05:09, Suren Baghdasaryan wrote: >>>>> On Mon, Sep 14, 2026 at 11:59 PM Hao Ge <[email protected]> wrote: >>>>>> >>>>>> The reservation is already stored in the maple tree when >>>>>> vm_module_tags_populate() fails. A failed load never unloads the >>>>>> module, so nothing releases the entry. Release it and roll >>>>>> module_tags.size back. Without the rollback a concurrent load that >>>>>> already passed needs_section_mem() can reuse the freed gap, skip >>>>>> vm_module_tags_populate() and write to unmapped memory. >>>>>> >>>>>> vmap_pages_range() may have installed some PTEs before failing. A >>>>>> retry to populate the same range would BUG on them, so undo them, >>>>>> but only if vmap actually ran. >>>>>> >>>>>> Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag >>>>>> compression") >>>>>> Fixes: 0f9b685626da ("alloc_tag: populate memory for module tags as >>>>>> needed") >>>>> >>>>> If a patch fixes two other patches, it likely needs to be split so >>>>> that each part fixes one patch only. But read on please. I'm not sure >>>>> if one of the fixes is correct. >>>>> >>>> >>>> Kept them in one patch because they only make sense together. >>>> >>>> After a failed populate the reservation is released and the >>>> size rolled back, so the next load takes the same gap and calls >>>> vm_module_tags_populate() again, and that retry would trip over >>>> the PTEs the failed vmap left behind. >>>> >>>> Without the rollback a load that already passed needs_section_mem() >>>> just reuses the gap, skips populate and writes to unmapped memory. >>>> So splitting them leaves each half broken. >>> >>> Yeah, that's why I think vmap_pages_range() cleanup should be a >>> completely separate patch with vmap_pages_range() doing cleanup >>> itself. >>> > > I think I get where you're coming from now. > Thanks for taking the time to explain. > >>>> >>>>>> Reported-by: Sashiko <[email protected]> >>>>>> Cc: [email protected] >>>>>> Signed-off-by: Hao Ge <[email protected]> >>>>>> --- >>>>>> mm/alloc_tag.c | 10 ++++++++++ >>>>>> 1 file changed, 10 insertions(+) >>>>>> >>>>>> diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c >>>>>> index 2070e682fe10..95ddf5b743d0 100644 >>>>>> --- a/mm/alloc_tag.c >>>>>> +++ b/mm/alloc_tag.c >>>>>> @@ -804,6 +804,13 @@ static int vm_module_tags_populate(void) >>>>>> next_page, PAGE_SHIFT) < 0) { >>>>>> release_pages_arg arg = { .pages = next_page }; >>>>>> >>>>>> + /* >>>>>> + * vmap_pages_range() only runs once all pages >>>>>> were >>>>>> + * allocated, and it may have installed some >>>>>> mappings >>>>>> + * before failing. Undo them. >>>>> >>>>> If vmap_pages_range() failed to map the range, why should we need to >>>>> undo it? If it indeed leaves some partial mapping when failing then I >>>>> would argue that vmap_pages_range() should be undoing these partial >>>>> mappings itself before returning the error. >>>>> >>>> Yeah it does - none of the paths under vmap_pages_range() undo themselves >>>> on error. >>> >>> Hmm. I wonder if this behavior is intentional or requires a fix. The >>> only possible reason I can think of is performance but I can't imagine >>> a failure to map is a performance-critical case. >>> >>> +David Hildenbrand (Red Hat), +Lorenzo Stoakes (Oracle) what do you >> >> Huh, my gmail thinks you are still at your previous companies :) >> > > I manually fixed it on the mailing list for this thread. > >>> guys think? Shouldn't vmap_pages_range() undo its possible partial >>> mapping when it fails? >>> >>> >>>> pcpu_map_pages does perform cleanup on its own as well. There may be other >>>> similar sites. >>>> https://elixir.bootlin.com/linux/v7.3-rc3/source/mm/percpu-vm.c#L255 >>>> so I did the same here. >>>> >>>> If we really want vmap_pages_range() to handle this cleanup internally, I >>>> believe that would >>>> be a relatively large change, and we would need to consider many more >>>> cases. So I think we keep >>>> the current behaviour for now. >>> >>> Yeah, I understand it would require a deeper cut but if that's the >>> right way to handle this we might as well do that. Let's see what MM >>> folks think. >>> > > Sounds good to me. Let's wait and hear what the MM folks say. >
I just looked into the call sites for __vmap_pages_range. And I found there's a bug in one vmalloc caller [1]. When gfp_mask has __GFP_NOFAIL, the code keeps retrying __vmap_pages_range. If there are leftover PTE mappings, this can trigger a BUG(); [2] https://elixir.bootlin.com/linux/v7.3-rc3/source/mm/vmalloc.c#L3946 [1] https://elixir.bootlin.com/linux/v7.3-rc3/source/mm/vmalloc.c#L121 [2] > Thanks > Best Regards > Hao > >>>> >>>> Thanks >>>> Best Regards >>>> Hao >>>> >>>>>> + */ >>>>>> + if (nr == more_pages) >>>>>> + vunmap_range(phys_end, phys_end + (nr << >>>>>> PAGE_SHIFT)); >>>>>> /* Clean up and error out */ >>>>>> release_pages(arg, nr); >>>>>> return -ENOMEM; >>>>>> @@ -947,6 +954,7 @@ static void *reserve_module_tags(struct module *mod, >>>>>> unsigned long size, >>>>>> return ret; >>>>>> >>>>>> if (module_tags.size < offset + size) { >>>>>> + unsigned long prev_size = module_tags.size; >>>>>> int grow_res; >>>>>> >>>>>> module_tags.size = offset + size; >>>>>> @@ -961,6 +969,8 @@ static void *reserve_module_tags(struct module *mod, >>>>>> unsigned long size, >>>>>> shutdown_mem_profiling(true); >>>>>> pr_err("Failed to allocate memory for allocation >>>>>> tags in the module %s. Memory allocation profiling is disabled!\n", >>>>>> mod->name); >>>>>> + release_module_tags(mod, false); >>>>>> + module_tags.size = prev_size; >>>>> >>>>> Yes, this one is a valid fix. It fixes 0f9b685626da commit. >>>>> >>>>>> return ERR_PTR(grow_res); >>>>>> } >>>>>> } >>>>>> -- >>>>>> 2.25.1 >>>>>>
