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    Subject[PATCH v5 09/10] mmap locking API: add mmap_assert_locked
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    Add mmap_assert_locked to assert that mmap_sem is held.

    Signed-off-by: Michel Lespinasse <walken@google.com>
    ---
    fs/userfaultfd.c | 6 +++---
    include/linux/mmap_lock.h | 10 ++++++++++
    mm/gup.c | 2 +-
    mm/memory.c | 2 +-
    4 files changed, 15 insertions(+), 5 deletions(-)

    diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
    index 9c645eee1a59..12b492409040 100644
    --- a/fs/userfaultfd.c
    +++ b/fs/userfaultfd.c
    @@ -234,7 +234,7 @@ static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
    pte_t *ptep, pte;
    bool ret = true;

    - VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
    + mmap_assert_locked(mm);

    ptep = huge_pte_offset(mm, address, vma_mmu_pagesize(vma));

    @@ -286,7 +286,7 @@ static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
    pte_t *pte;
    bool ret = true;

    - VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
    + mmap_assert_locked(mm);

    pgd = pgd_offset(mm, address);
    if (!pgd_present(*pgd))
    @@ -405,7 +405,7 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
    * Coredumping runs without mmap_sem so we can only check that
    * the mmap_sem is held, if PF_DUMPCORE was not set.
    */
    - WARN_ON_ONCE(!rwsem_is_locked(&mm->mmap_sem));
    + mmap_assert_locked(mm);

    ctx = vmf->vma->vm_userfaultfd_ctx.ctx;
    if (!ctx)
    diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
    index 9e104835a0d1..f7a3a9550cc5 100644
    --- a/include/linux/mmap_lock.h
    +++ b/include/linux/mmap_lock.h
    @@ -1,6 +1,8 @@
    #ifndef _LINUX_MMAP_LOCK_H
    #define _LINUX_MMAP_LOCK_H

    +#include <linux/mmdebug.h>
    +
    #define MMAP_LOCK_INITIALIZER(name) \
    .mmap_sem = __RWSEM_INITIALIZER(name.mmap_sem),

    @@ -73,4 +75,12 @@ static inline void mmap_read_unlock_non_owner(struct mm_struct *mm)
    up_read_non_owner(&mm->mmap_sem);
    }

    +static inline void mmap_assert_locked(struct mm_struct *mm)
    +{
    + if (IS_ENABLED(CONFIG_LOCKDEP) && debug_locks)
    + VM_BUG_ON_MM(!lockdep_is_held(&mm->mmap_sem), mm);
    + else
    + VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm);
    +}
    +
    #endif /* _LINUX_MMAP_LOCK_H */
    diff --git a/mm/gup.c b/mm/gup.c
    index 0404e52513b2..e12993ceb711 100644
    --- a/mm/gup.c
    +++ b/mm/gup.c
    @@ -1403,7 +1403,7 @@ long populate_vma_page_range(struct vm_area_struct *vma,
    VM_BUG_ON(end & ~PAGE_MASK);
    VM_BUG_ON_VMA(start < vma->vm_start, vma);
    VM_BUG_ON_VMA(end > vma->vm_end, vma);
    - VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm);
    + mmap_assert_locked(mm);

    gup_flags = FOLL_TOUCH | FOLL_POPULATE | FOLL_MLOCK;
    if (vma->vm_flags & VM_LOCKONFAULT)
    diff --git a/mm/memory.c b/mm/memory.c
    index e6dd3309c5a3..20f98ea8968e 100644
    --- a/mm/memory.c
    +++ b/mm/memory.c
    @@ -1214,7 +1214,7 @@ static inline unsigned long zap_pud_range(struct mmu_gather *tlb,
    next = pud_addr_end(addr, end);
    if (pud_trans_huge(*pud) || pud_devmap(*pud)) {
    if (next - addr != HPAGE_PUD_SIZE) {
    - VM_BUG_ON_VMA(!rwsem_is_locked(&tlb->mm->mmap_sem), vma);
    + mmap_assert_locked(tlb->mm);
    split_huge_pud(vma, pud, addr);
    } else if (zap_huge_pud(tlb, vma, pud, addr))
    goto next;
    --
    2.26.1.301.g55bc3eb7cb9-goog
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