On Mon, Sep 28, 2026 at 8:09 AM Uladzislau Rezki <[email protected]> wrote: > > On Mon, Sep 28, 2026 at 01:09:13PM +0200, Uladzislau Rezki wrote: > > 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] > > > > > Indeed the below code is incomplete: > > > > <snip> > > /* > > * page tables allocations ignore external gfp mask, enforce it > > * by the scope API > > */ > > flags = memalloc_apply_gfp_scope(gfp_mask); > > do { > > ret = __vmap_pages_range(addr, addr + size, prot, area->pages, > > page_shift, nested_gfp); > > if (nofail && (ret < 0)) > > schedule_timeout_uninterruptible(1); > > } while (nofail && (ret < 0)); > > memalloc_restore_scope(flags); > > <snip> > > > > and it should be fixed. As the __vmap_pages_range() can actually fail > > and leave some installed mappings, we have to perform some cleanups > > on failure or on repeat(if nofail is true). > > > > Below code: > > > > + /* > > + * vmap_pages_range() only runs once all pages were > > + * allocated, and it may have installed some mappings > > + * before failing. Undo them. > > + */ > > + if (nr == more_pages) > > + vunmap_range(phys_end, phys_end + (nr << > > PAGE_SHIFT)); > > > > we can use but we need to check if partially mapped space is not an > > issue for the vunmap_range(). And it looks like it is not. > > > > <snip> > > @@ -3953,8 +3990,15 @@ static void *__vmalloc_area_node(struct vm_struct > > *area, gfp_t gfp_mask, > > do { > > ret = __vmap_pages_range(addr, addr + size, prot, > > area->pages, > > page_shift, nested_gfp); > > - if (nofail && (ret < 0)) > > - schedule_timeout_uninterruptible(1); > > + if (ret < 0) { > > + /* > > + * __vmap_pages_range() may have installed some > > mappings > > + * before failing. Undo them before returning or > > retrying. > > + */ > > + vunmap_range(addr, addr + size); > > + if (nofail) > > + schedule_timeout_uninterruptible(1); > > + } > > } while (nofail && (ret < 0)); > > memalloc_restore_scope(flags); > > <snip> > > > And looking further. If the __vmap_pages_range()/__vmap_pages_range_noflush() > and friends fail, a proper cleanups should be done inside, IMO.
Sounds like we are in agreement. > > But i am checking callers and see that some do some not: > > <snip hooks.c> > __vunmap_range_noflush( > vmalloc_shadow(start), > vmalloc_shadow(start + clean * PAGE_SIZE)); > __vunmap_range_noflush( > vmalloc_origin(start), > vmalloc_origin(start + clean * PAGE_SIZE)); > <snip hooks.c> > > kmsan_ioremap_page_range() it does clean ups; > kmsan_vmap_pages_range_noflush() looks like does not care in shadow.c; > __vmalloc_area_node() as noted, it is broken as there is a BUG() on next try > if nofail; > pcpu_map_pages() it does cleanups. > ... > > and so on. Yeah, the callers that do the cleanup should stop doing that once the vmap functions handle it themselves. I expect an overall reduction in code size. > > -- > Uladzislau Rezki
