diff options
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/mm.h | 5 | ||||
| -rw-r--r-- | include/linux/mmap_lock.h | 52 |
2 files changed, 53 insertions, 4 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h index aa90719234f1..2c6c6d00ed73 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1008,10 +1008,7 @@ static inline void vma_flag_set_atomic(struct vm_area_struct *vma, { unsigned long *bitmap = ACCESS_PRIVATE(&vma->flags, __vma_flags); - /* mmap read lock/VMA read lock must be held. */ - if (!rwsem_is_locked(&vma->vm_mm->mmap_lock)) - vma_assert_locked(vma); - + vma_assert_stabilised(vma); if (__vma_flag_atomic_valid(vma, bit)) set_bit((__force int)bit, bitmap); } diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h index 90fc32b683dd..93eca48bc443 100644 --- a/include/linux/mmap_lock.h +++ b/include/linux/mmap_lock.h @@ -374,6 +374,52 @@ static inline void vma_assert_locked(struct vm_area_struct *vma) vma_assert_write_locked(vma); } +/** + * vma_assert_stabilised() - assert that this VMA cannot be changed from + * underneath us either by having a VMA or mmap lock held. + * @vma: The VMA whose stability we wish to assess. + * + * If lockdep is enabled we can precisely ensure stability via either an mmap + * lock owned by us or a specific VMA lock. + * + * With lockdep disabled we may sometimes race with other threads acquiring the + * mmap read lock simultaneous with our VMA read lock. + */ +static inline void vma_assert_stabilised(struct vm_area_struct *vma) +{ + /* + * If another thread owns an mmap lock, it may go away at any time, and + * thus is no guarantee of stability. + * + * If lockdep is enabled we can accurately determine if an mmap lock is + * held and owned by us. Otherwise we must approximate. + * + * It doesn't necessarily mean we are not stabilised however, as we may + * hold a VMA read lock (not a write lock as this would require an owned + * mmap lock). + * + * If (assuming lockdep is not enabled) we were to assert a VMA read + * lock first we may also run into issues, as other threads can hold VMA + * read locks simlutaneous to us. + * + * Therefore if lockdep is not enabled we risk a false negative (i.e. no + * assert fired). If accurate checking is required, enable lockdep. + */ + if (IS_ENABLED(CONFIG_LOCKDEP)) { + if (lockdep_is_held(&vma->vm_mm->mmap_lock)) + return; + } else { + if (rwsem_is_locked(&vma->vm_mm->mmap_lock)) + return; + } + + /* + * We're not stabilised by the mmap lock, so assert that we're + * stabilised by a VMA lock. + */ + vma_assert_locked(vma); +} + static inline bool vma_is_attached(struct vm_area_struct *vma) { return refcount_read(&vma->vm_refcnt); @@ -476,6 +522,12 @@ static inline void vma_assert_locked(struct vm_area_struct *vma) mmap_assert_locked(vma->vm_mm); } +static inline void vma_assert_stabilised(struct vm_area_struct *vma) +{ + /* If no VMA locks, then either mmap lock suffices to stabilise. */ + mmap_assert_locked(vma->vm_mm); +} + #endif /* CONFIG_PER_VMA_LOCK */ static inline void mmap_write_lock(struct mm_struct *mm) |