On Wed, Jan 14, 2026 at 10:42 AM Pratyush Yadav <[email protected]> wrote: > > On Wed, Jan 14 2026, Suren Baghdasaryan wrote: > > > On Wed, Jan 14, 2026 at 8:55 AM Pratyush Yadav <[email protected]> wrote: > >> > >> Hi Ran, > >> > >> On Tue, Jan 13 2026, [email protected] wrote: > >> > >> > From: Ran Xiaokai <[email protected]> > >> > > >> > Memblock pages (including reserved memory) should have their allocation > >> > tags initialized to CODETAG_EMPTY via clear_page_tag_ref() before being > >> > released to the page allocator. When kho restores pages through > >> > kho_restore_page(), missing this call causes mismatched > >> > allocation/deallocation tracking and below warning message: > >> > alloc_tag was not set > >> > WARNING: include/linux/alloc_tag.h:164 at ___free_pages+0xb8/0x260, > >> > CPU#1: swapper/0/1 > >> > RIP: 0010:___free_pages+0xb8/0x260 > >> > kho_restore_vmalloc+0x187/0x2e0 > >> > kho_test_init+0x3c4/0xa30 > >> > do_one_initcall+0x62/0x2b0 > >> > kernel_init_freeable+0x25b/0x480 > >> > kernel_init+0x1a/0x1c0 > >> > ret_from_fork+0x2d1/0x360 > >> > > >> > Add missing clear_page_tag_ref() annotation in kho_restore_page() to > >> > fix this. > >> > > >> > Fixes: fc33e4b44b27 ("kexec: enable KHO support for memory preservation") > >> > Signed-off-by: Ran Xiaokai <[email protected]> > >> > Reviewed-by: Mike Rapoport (Microsoft) <[email protected]> > >> > Reviewed-by: Suren Baghdasaryan <[email protected]> > >> > --- > >> > kernel/liveupdate/kexec_handover.c | 1 + > >> > 1 file changed, 1 insertion(+) > >> > > >> > diff --git a/kernel/liveupdate/kexec_handover.c > >> > b/kernel/liveupdate/kexec_handover.c > >> > index cd6b3fb9dcae..2d47f2c50bd8 100644 > >> > --- a/kernel/liveupdate/kexec_handover.c > >> > +++ b/kernel/liveupdate/kexec_handover.c > >> > @@ -268,6 +268,7 @@ static struct page *kho_restore_page(phys_addr_t > >> > phys, bool is_folio) > >> > else > >> > kho_init_pages(page, nr_pages); > >> > > >> > + clear_page_tag_ref(page); > >> > >> You are only clearing the tag for the head page. The tail pages are > >> still un-initialized. Is that intentional? > > > > In the case of a compound page we set the tag only on the head page, > > so this is correct. > > > >> > >> What about non-compound pages (the ones you get from > >> kho_restore_pages(), aka when is_folio is false)? Do we need to clear > >> the tag on all pages in that case? > > > > In the case of kho_restore_pages() we call split_page() which calls > > Not since 7b71205ae112 ("kho: fix restoring of contiguous ranges of > order-0 pages"). That commit removed the split_pages() call and > open-coded the page initialization logic tailored for KHO.
Ah, I see. I missed that change. > > So I think you do need to initialize the tags for kho_restore_pages(). > > I sent a patch [0] simplifying the page init logic a bit. I need to do a > v2 but it is a very simple change so I can get that done tomorrow. I > think it would be good to base your series on that since that would make > it easier for you to modify only the kho_restore_pages() path and the > end result would be cleaner. > > [0] > https://lore.kernel.org/linux-mm/[email protected]/ Ok, let's wait for your patch to see the final result. Please CC us when you send it. > > > pgalloc_tag_split() and that propagates the tag from the head page to > > all the tail pages being split from it. However now that I'm looking > > at it, I'm not sure pgalloc_tag_split() works correctly if the tag > > reference of the head page is CODETAG_EMPTY. In summary, this patch is > > fine but there might be a bug inside pgalloc_tag_split() if the tag > > reference is CODETAG_EMPTY. > > > > I'll analyze and reproduce that case. If it indeed has the issue I > > think it's easy to fix it by creating a specialized alloc_tag object > > with alloc_tag->ct=CODETAG_EMPTY and make __pgalloc_tag_get() return > > it if the page's tag reference is CODETAG_EMPTY. > > > >> > >> > adjust_managed_page_count(page, nr_pages); > >> > return page; > >> > }
