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owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Nov 10, 2025 at 07:15:53PM +0800, Lance Yang wrote: > From: Lance Yang > > The hugetlb VMA unmap path contains several potential deadlocks, as > reported by syzbot. These deadlocks occur in __hugetlb_zap_begin(), > move_hugetlb_page_tables(), and the retry path of > hugetlb_unmap_file_folio() (affecting remove_inode_hugepages() and > unmap_vmas()), where vma_lock is acquired before i_mmap_lock. This lock > ordering conflicts with other paths like hugetlb_fault(), which establish > the correct dependency as i_mmap_lock -> vma_lock. > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(&vma_lock->rw_sema); > lock(&i_mmap_lock); > lock(&vma_lock->rw_sema); > lock(&i_mmap_lock); > > Resolve the circular dependencies reported by syzbot across multiple call > chains by reordering the locks in all conflicting paths to consistently > follow the established i_mmap_lock -> vma_lock order. But mm/rmap.c says: > * hugetlbfs PageHuge() take locks in this order: > * hugetlb_fault_mutex (hugetlbfs specific page fault mutex) > * vma_lock (hugetlb specific lock for pmd_sharing) > * mapping->i_mmap_rwsem (also used for hugetlb pmd sharing) > * folio_lock > */ I think the commit message should explain why the locking order described above is incorrect (or when it became incorrect) and fix the comment? > Reported-by: syzbot+3f5f9a0d292454409ca6@syzkaller.appspotmail.com > Closes: https://lore.kernel.org/linux-mm/69113a97.a70a0220.22f260.00ca.GAE@google.com/ > Signed-off-by: Lance Yang > --- > V1 -> V2: > - Update changelog > - Resolve three related deadlock scenarios reported by syzbot > https://lore.kernel.org/linux-mm/6911ad38.a70a0220.22f260.00dc.GAE@google.com/ > - https://lore.kernel.org/linux-mm/20251110051421.29436-1-lance.yang@linux.dev/ > > fs/hugetlbfs/inode.c | 2 +- > mm/hugetlb.c | 4 ++-- > 2 files changed, 3 insertions(+), 3 deletions(-) > > diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c > index 3919fca56553..d1b0b5346728 100644 > --- a/fs/hugetlbfs/inode.c > +++ b/fs/hugetlbfs/inode.c > @@ -447,8 +447,8 @@ static void hugetlb_unmap_file_folio(struct hstate *h, > * a reference. We must 'open code' vma locking as we do > * not know if vma_lock is still attached to vma. > */ > - down_write(&vma_lock->rw_sema); > i_mmap_lock_write(mapping); > + down_write(&vma_lock->rw_sema); > > vma = vma_lock->vma; > if (!vma) { > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index b1f47b87ae65..f0212d2579f6 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -5110,8 +5110,8 @@ int move_hugetlb_page_tables(struct vm_area_struct *vma, > mmu_notifier_invalidate_range_start(&range); > last_addr_mask = hugetlb_mask_last_page(h); > /* Prevent race with file truncation */ > - hugetlb_vma_lock_write(vma); > i_mmap_lock_write(mapping); > + hugetlb_vma_lock_write(vma); > for (; old_addr < old_end; old_addr += sz, new_addr += sz) { > src_pte = hugetlb_walk(vma, old_addr, sz); > if (!src_pte) { > @@ -5327,9 +5327,9 @@ void __hugetlb_zap_begin(struct vm_area_struct *vma, > return; > > adjust_range_if_pmd_sharing_possible(vma, start, end); > - hugetlb_vma_lock_write(vma); > if (vma->vm_file) > i_mmap_lock_write(vma->vm_file->f_mapping); > + hugetlb_vma_lock_write(vma); > } > > void __hugetlb_zap_end(struct vm_area_struct *vma, > -- > 2.49.0 > > -- Cheers, Harry / Hyeonggon