Re: [PATCH RESEND v3 04/10] mm/vma: add+use vma lockdep acquire/release defines

Vlastimil Babka
2026-01-23T08:48:30Z

On 1/22/26 14:01, Lorenzo Stoakes wrote:
> The code is littered with inscrutable and duplicative lockdep incantations,
> replace these with defines which explain what is going on and add
> commentary to explain what we're doing.
>
> If lockdep is disabled these become no-ops. We must use defines so _RET_IP_
> remains meaningful.
>
> These are self-documenting and aid readability of the code.
>
> Additionally, instead of using the confusing rwsem_*() form for something
> that is emphatically not an rwsem, we instead explicitly use
> lock_[acquired, release]_shared/exclusive() lockdep invocations since we
> are doing something rather custom here and these make more sense to use.
>
> No functional change intended.
>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

Reviewed-by: Vlastimil Babka <vbabka@suse.cz>

Nits:

> ---
> include/linux/mmap_lock.h | 35 ++++++++++++++++++++++++++++++++---
> mm/mmap_lock.c | 10 +++++-----
> 2 files changed, 37 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
> index 0b3614aadbb4..da63b1be6ec0 100644
> --- a/include/linux/mmap_lock.h
> +++ b/include/linux/mmap_lock.h
> @@ -78,6 +78,36 @@ static inline void mmap_assert_write_locked(const struct mm_struct *mm)
>
> #ifdef CONFIG_PER_VMA_LOCK
>
> +/*
> + * VMA locks do not behave like most ordinary locks found in the kernel, so we
> + * cannot quite have full lockdep tracking in the way we would ideally prefer.
> + *
> + * Read locks act as shared locks which exclude an exclusive lock being
> + * taken. We therefore mark these accordingly on read lock acquire/release.
> + *
> + * Write locks are acquired exclusively per-VMA, but released in a shared
> + * fashion, that is upon vma_end_write_all(), we update the mmap's seqcount such
> + * that write lock is de-acquired.

de-acquired -> released?

> + * We therefore cannot track write locks per-VMA, nor do we try. Mitigating this
> + * is the fact that, of course, we do lockdep-track the mmap lock rwsem.

"... which has to be held in order to take a VMA write lock" ?

> + * We do, however, want to indicate that during either acquisition of a VMA
> + * write lock or detachment of a VMA that we require the lock held be exclusive,
> + * so we utilise lockdep to do so.
> + */
> +#define __vma_lockdep_acquire_read(vma) \
> + lock_acquire_shared(&vma->vmlock_dep_map, 0, 1, NULL, _RET_IP_)
> +#define __vma_lockdep_release_read(vma) \
> + lock_release(&vma->vmlock_dep_map, _RET_IP_)
> +#define __vma_lockdep_acquire_exclusive(vma) \
> + lock_acquire_exclusive(&vma->vmlock_dep_map, 0, 0, NULL, _RET_IP_)
> +#define __vma_lockdep_release_exclusive(vma) \
> + lock_release(&vma->vmlock_dep_map, _RET_IP_)
> +/* Only meaningful if CONFIG_LOCK_STAT is defined. */
> +#define __vma_lockdep_stat_mark_acquired(vma) \
> + lock_acquired(&vma->vmlock_dep_map, _RET_IP_)
> +
> static inline void mm_lock_seqcount_init(struct mm_struct *mm)
> {
> seqcount_init(&mm->mm_lock_seq);
> @@ -176,8 +206,7 @@ static inline void vma_refcount_put(struct vm_area_struct *vma)
> int refcnt;
> bool detached;
>
> - rwsem_release(&vma->vmlock_dep_map, _RET_IP_);
> -
> + __vma_lockdep_release_read(vma);
> detached = __vma_refcount_put(vma, &refcnt);
> /*
> * __vma_enter_locked() may be sleeping waiting for readers to drop
> @@ -203,7 +232,7 @@ static inline bool vma_start_read_locked_nested(struct vm_area_struct *vma, int
> VM_REFCNT_LIMIT)))
> return false;
>
> - rwsem_acquire_read(&vma->vmlock_dep_map, 0, 1, _RET_IP_);
> + __vma_lockdep_acquire_read(vma);
> return true;
> }
>
> diff --git a/mm/mmap_lock.c b/mm/mmap_lock.c
> index ebacb57e5f16..9563bfb051f4 100644
> --- a/mm/mmap_lock.c
> +++ b/mm/mmap_lock.c
> @@ -72,7 +72,7 @@ static inline int __vma_enter_locked(struct vm_area_struct *vma,
> if (!refcount_add_not_zero(VM_REFCNT_EXCLUDE_READERS_FLAG, &vma->vm_refcnt))
> return 0;
>
> - rwsem_acquire(&vma->vmlock_dep_map, 0, 0, _RET_IP_);
> + __vma_lockdep_acquire_exclusive(vma);
> err = rcuwait_wait_event(&vma->vm_mm->vma_writer_wait,
> refcount_read(&vma->vm_refcnt) == tgt_refcnt,
> state);
> @@ -85,10 +85,10 @@ static inline int __vma_enter_locked(struct vm_area_struct *vma,
> WARN_ON_ONCE(!detaching);
> err = 0;
> }
> - rwsem_release(&vma->vmlock_dep_map, _RET_IP_);
> + __vma_lockdep_release_exclusive(vma);
> return err;
> }
> - lock_acquired(&vma->vmlock_dep_map, _RET_IP_);
> + __vma_lockdep_stat_mark_acquired(vma);
>
> return 1;
> }
> @@ -97,7 +97,7 @@ static inline void __vma_exit_locked(struct vm_area_struct *vma, bool *detached)
> {
> *detached = refcount_sub_and_test(VM_REFCNT_EXCLUDE_READERS_FLAG,
> &vma->vm_refcnt);
> - rwsem_release(&vma->vmlock_dep_map, _RET_IP_);
> + __vma_lockdep_release_exclusive(vma);
> }
>
> int __vma_start_write(struct vm_area_struct *vma, unsigned int mm_lock_seq,
> @@ -199,7 +199,7 @@ static inline struct vm_area_struct *vma_start_read(struct mm_struct *mm,
> goto err;
> }
>
> - rwsem_acquire_read(&vma->vmlock_dep_map, 0, 1, _RET_IP_);
> + __vma_lockdep_acquire_read(vma);
>
> if (unlikely(vma->vm_mm != mm))
> goto err_unstable;
> --
> 2.52.0