Hi Suren and Uladzislau On 2026/9/29 01:54, Suren Baghdasaryan wrote: > On Mon, Sep 28, 2026 at 10:47 AM Uladzislau Rezki <[email protected]> wrote: >> >> On Mon, Sep 28, 2026 at 08:16:18AM -0700, Suren Baghdasaryan wrote: >>> 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. >>> >> Agree. If mapping API is called and it fails the caller should expect >> the state as it was before calling that API function, IMO. > > Thanks for confirmation! > > Hao, do you need help with making the change in vmap functions to > cleanup upon a failure? >
Thanks everyone for your help. I think we have reached a consensus. I spent a day sorting out the logic and generated the patches below: https://lore.kernel.org/all/[email protected]/ Some edge cases might still be missing, please kindly review. Thanks Best Regards Hao >> >> -- >> Uladzislau Rezki
