From 14967a9c7d247841b0312c48dcf8cd29e55a4cc8 Mon Sep 17 00:00:00 2001 From: Jane Chu Date: Mon, 15 Sep 2025 18:45:20 -0600 Subject: mm/hugetlb: fix copy_hugetlb_page_range() to use ->pt_share_count commit 59d9094df3d79 ("mm: hugetlb: independent PMD page table shared count") introduced ->pt_share_count dedicated to hugetlb PMD share count tracking, but omitted fixing copy_hugetlb_page_range(), leaving the function relying on page_count() for tracking that no longer works. When lazy page table copy for hugetlb is disabled, that is, revert commit bcd51a3c679d ("hugetlb: lazy page table copies in fork()") fork()'ing with hugetlb PMD sharing quickly lockup - [ 239.446559] watchdog: BUG: soft lockup - CPU#75 stuck for 27s! [ 239.446611] RIP: 0010:native_queued_spin_lock_slowpath+0x7e/0x2e0 [ 239.446631] Call Trace: [ 239.446633] [ 239.446636] _raw_spin_lock+0x3f/0x60 [ 239.446639] copy_hugetlb_page_range+0x258/0xb50 [ 239.446645] copy_page_range+0x22b/0x2c0 [ 239.446651] dup_mmap+0x3e2/0x770 [ 239.446654] dup_mm.constprop.0+0x5e/0x230 [ 239.446657] copy_process+0xd17/0x1760 [ 239.446660] kernel_clone+0xc0/0x3e0 [ 239.446661] __do_sys_clone+0x65/0xa0 [ 239.446664] do_syscall_64+0x82/0x930 [ 239.446668] ? count_memcg_events+0xd2/0x190 [ 239.446671] ? syscall_trace_enter+0x14e/0x1f0 [ 239.446676] ? syscall_exit_work+0x118/0x150 [ 239.446677] ? arch_exit_to_user_mode_prepare.constprop.0+0x9/0xb0 [ 239.446681] ? clear_bhb_loop+0x30/0x80 [ 239.446684] ? clear_bhb_loop+0x30/0x80 [ 239.446686] entry_SYSCALL_64_after_hwframe+0x76/0x7e There are two options to resolve the potential latent issue: 1. warn against PMD sharing in copy_hugetlb_page_range(), 2. fix it. This patch opts for the second option. While at it, simplify the comment, the details are not actually relevant anymore. Link: https://lkml.kernel.org/r/20250916004520.1604530-1-jane.chu@oracle.com Fixes: 59d9094df3d7 ("mm: hugetlb: independent PMD page table shared count") Signed-off-by: Jane Chu Reviewed-by: Harry Yoo Acked-by: Oscar Salvador Acked-by: David Hildenbrand Cc: Jann Horn Cc: Liu Shixin Cc: Muchun Song Signed-off-by: Andrew Morton --- include/linux/mm_types.h | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'include/linux') diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 08bc2442db93..a643fae8a349 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -631,6 +631,11 @@ static inline int ptdesc_pmd_pts_count(struct ptdesc *ptdesc) { return atomic_read(&ptdesc->pt_share_count); } + +static inline bool ptdesc_pmd_is_shared(struct ptdesc *ptdesc) +{ + return !!ptdesc_pmd_pts_count(ptdesc); +} #else static inline void ptdesc_pmd_pts_init(struct ptdesc *ptdesc) { -- cgit v1.2.3 From 7e89979f6695fb56e8739b7d19614256e637131d Mon Sep 17 00:00:00 2001 From: Andrew Morton Date: Sat, 13 Sep 2025 17:03:39 -0700 Subject: include/linux/pgtable.h: convert arch_enter_lazy_mmu_mode() and friends to static inlines commit c519c3c0a113 ("mm/kasan: avoid lazy MMU mode hazards") introduced the use of arch_enter_lazy_mmu_mode(), which results in the compiler complaining about "statement has no effect", when __HAVE_ARCH_LAZY_MMU_MODE is not defined in include/linux/pgtable.h The exact warning/error is: In file included from ./include/linux/kasan.h:37, from mm/kasan/shadow.c:14: mm/kasan/shadow.c: In function kasan_populate_vmalloc_pte: ./include/linux/pgtable.h:247:41: error: statement with no effect [-Werror=unused-value] 247 | #define arch_enter_lazy_mmu_mode() (LAZY_MMU_DEFAULT) | ^ mm/kasan/shadow.c:322:9: note: in expansion of macro arch_enter_lazy_mmu_mode> 322 | arch_enter_lazy_mmu_mode(); | ^~~~~~~~~~~~~~~~~~~~~~~~ switching these "functions" to static inlines fixes this up. Fixes: c519c3c0a113 ("mm/kasan: avoid lazy MMU mode hazards") Reported-by: Balbir Singh Closes: https://lkml.kernel.org/r/20250912235515.367061-1-balbirs@nvidia.com Cc: Alexander Gordeev Cc: Andrey Ryabinin Signed-off-by: Andrew Morton --- include/linux/pgtable.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'include/linux') diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h index 2b80fd456c8b..25a7257052ff 100644 --- a/include/linux/pgtable.h +++ b/include/linux/pgtable.h @@ -232,9 +232,9 @@ static inline int pmd_dirty(pmd_t pmd) * and the mode cannot be used in interrupt context. */ #ifndef __HAVE_ARCH_ENTER_LAZY_MMU_MODE -#define arch_enter_lazy_mmu_mode() do {} while (0) -#define arch_leave_lazy_mmu_mode() do {} while (0) -#define arch_flush_lazy_mmu_mode() do {} while (0) +static inline void arch_enter_lazy_mmu_mode(void) {} +static inline void arch_leave_lazy_mmu_mode(void) {} +static inline void arch_flush_lazy_mmu_mode(void) {} #endif #ifndef pte_batch_hint -- cgit v1.2.3