Looping in Ulad who is best placed to respond on this. Ulad could you look at the below? Thanks! :)
On Thu, Sep 17, 2026 at 10:32:48AM +0800, Hao Ge wrote: > 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] I think best person to look at this is Ulad as vmalloc is his baby :) Ulad, what do you think? Thread is at https://lore.kernel.org/all/[email protected]/ for context. > > > 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 > >>>>>> -- Cheers, Lorenzo
