Le 01/09/2022 à 19:35, Suren Baghdasaryan a écrit :
> Assert there are no holders of VMA lock for reading when it is about to be
> destroyed.
>
> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> ---
> include/linux/mm.h | 8 ++++++++
> kernel/fork.c | 2 ++
> 2 files changed, 10 insertions(+)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index dc72be923e5b..0d9c1563c354 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -676,6 +676,13 @@ static inline void vma_assert_write_locked(struct vm_area_struct *vma, int pos)
> VM_BUG_ON_VMA(vma->vm_lock_seq != READ_ONCE(vma->vm_mm->mm_lock_seq), vma);
> }
>
> +static inline void vma_assert_no_reader(struct vm_area_struct *vma)
> +{
> + VM_BUG_ON_VMA(rwsem_is_locked(&vma->lock) &&
> + vma->vm_lock_seq != READ_ONCE(vma->vm_mm->mm_lock_seq),
> + vma);
> +}
> +
> #else /* CONFIG_PER_VMA_LOCK */
>
> static inline void vma_init_lock(struct vm_area_struct *vma) {}
> @@ -685,6 +692,7 @@ static inline bool vma_read_trylock(struct vm_area_struct *vma)
> static inline void vma_read_unlock(struct vm_area_struct *vma) {}
> static inline void vma_assert_locked(struct vm_area_struct *vma) {}
> static inline void vma_assert_write_locked(struct vm_area_struct *vma, int pos) {}
> +static inline void vma_assert_no_reader(struct vm_area_struct *vma) {}
>
> #endif /* CONFIG_PER_VMA_LOCK */
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 1872ad549fed..b443ba3a247a 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -487,6 +487,8 @@ static void __vm_area_free(struct rcu_head *head)
> {
> struct vm_area_struct *vma = container_of(head, struct vm_area_struct,
> vm_rcu);
> + /* The vma should either have no lock holders or be write-locked. */
> + vma_assert_no_reader(vma);
I'm wondering if this can be hit in the case the thread freeing a VMA is
preempted before incrementing the mm ref count, like this:
VMA is about to be freed
write lock VMA
free vma -> call_rcu
..
<--- thread preempted
rcu handler runs
rcu calls __vm_area_free() <<<<<<
unlock mmap_lock and increase the mm seq count
> kmem_cache_free(vm_area_cachep, vma);
> }
> #endif
