Re: [Freedreno] [PATCH v3 06/23] drm/msm/gem: Move locking in shrinker path

Kristian Høgsberg
2020-10-23T08:55:57Z

On Mon, Oct 19, 2020 at 10:45 PM Rob Clark <robdclark@gmail.com> wrote:
>
> From: Rob Clark <robdclark@chromium.org>
>
> Move grabbing the bo lock into shrinker, with a msm_gem_trylock() to
> skip over bo's that are already locked. This gets rid of the nested
> lock classes.
>
> Signed-off-by: Rob Clark <robdclark@chromium.org>
> ---
> drivers/gpu/drm/msm/msm_gem.c | 24 +++++----------------
> drivers/gpu/drm/msm/msm_gem.h | 29 ++++++++++----------------
> drivers/gpu/drm/msm/msm_gem_shrinker.c | 27 +++++++++++++++++-------
> 3 files changed, 35 insertions(+), 45 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
> index e0d8d739b068..1195847714ba 100644
> --- a/drivers/gpu/drm/msm/msm_gem.c
> +++ b/drivers/gpu/drm/msm/msm_gem.c
> @@ -17,8 +17,6 @@
> #include "msm_gpu.h"
> #include "msm_mmu.h"
>
> -static void msm_gem_vunmap_locked(struct drm_gem_object *obj);
> -
>
> static dma_addr_t physaddr(struct drm_gem_object *obj)
> {
> @@ -693,20 +691,19 @@ int msm_gem_madvise(struct drm_gem_object *obj, unsigned madv)
> return (madv != __MSM_MADV_PURGED);
> }
>
> -void msm_gem_purge(struct drm_gem_object *obj, enum msm_gem_lock subclass)
> +void msm_gem_purge(struct drm_gem_object *obj)
> {
> struct drm_device *dev = obj->dev;
> struct msm_gem_object *msm_obj = to_msm_bo(obj);
>
> WARN_ON(!mutex_is_locked(&dev->struct_mutex));
> + WARN_ON(!msm_gem_is_locked(obj));
> WARN_ON(!is_purgeable(msm_obj));
> WARN_ON(obj->import_attach);
>
> - mutex_lock_nested(&msm_obj->lock, subclass);
> -
> put_iova(obj);
>
> - msm_gem_vunmap_locked(obj);
> + msm_gem_vunmap(obj);
>
> put_pages(obj);
>
> @@ -724,11 +721,9 @@ void msm_gem_purge(struct drm_gem_object *obj, enum msm_gem_lock subclass)
>
> invalidate_mapping_pages(file_inode(obj->filp)->i_mapping,
> 0, (loff_t)-1);
> -
> - msm_gem_unlock(obj);
> }
>
> -static void msm_gem_vunmap_locked(struct drm_gem_object *obj)
> +void msm_gem_vunmap(struct drm_gem_object *obj)
> {
> struct msm_gem_object *msm_obj = to_msm_bo(obj);
>
> @@ -741,15 +736,6 @@ static void msm_gem_vunmap_locked(struct drm_gem_object *obj)
> msm_obj->vaddr = NULL;
> }
>
> -void msm_gem_vunmap(struct drm_gem_object *obj, enum msm_gem_lock subclass)
> -{
> - struct msm_gem_object *msm_obj = to_msm_bo(obj);
> -
> - mutex_lock_nested(&msm_obj->lock, subclass);
> - msm_gem_vunmap_locked(obj);
> - msm_gem_unlock(obj);
> -}
> -
> /* must be called before _move_to_active().. */
> int msm_gem_sync_object(struct drm_gem_object *obj,
> struct msm_fence_context *fctx, bool exclusive)
> @@ -986,7 +972,7 @@ static void free_object(struct msm_gem_object *msm_obj)
>
> drm_prime_gem_destroy(obj, msm_obj->sgt);
> } else {
> - msm_gem_vunmap_locked(obj);
> + msm_gem_vunmap(obj);
> put_pages(obj);
> }
>
> diff --git a/drivers/gpu/drm/msm/msm_gem.h b/drivers/gpu/drm/msm/msm_gem.h
> index d55d5401a2d2..c5232b8da794 100644
> --- a/drivers/gpu/drm/msm/msm_gem.h
> +++ b/drivers/gpu/drm/msm/msm_gem.h
> @@ -162,6 +162,13 @@ msm_gem_lock(struct drm_gem_object *obj)
> mutex_lock(&msm_obj->lock);
> }
>
> +static inline bool __must_check
> +msm_gem_trylock(struct drm_gem_object *obj)
> +{
> + struct msm_gem_object *msm_obj = to_msm_bo(obj);
> + return mutex_trylock_recursive(&msm_obj->lock) == MUTEX_TRYLOCK_SUCCESS;

This can just be

return mutex_trylock(&msm_obj->lock) == 1;

now, right?

> +}
> +
> static inline int
> msm_gem_lock_interruptible(struct drm_gem_object *obj)
> {
> @@ -190,6 +197,7 @@ static inline bool is_active(struct msm_gem_object *msm_obj)
>
> static inline bool is_purgeable(struct msm_gem_object *msm_obj)
> {
> + WARN_ON(!msm_gem_is_locked(&msm_obj->base));
> WARN_ON(!mutex_is_locked(&msm_obj->base.dev->struct_mutex));
> return (msm_obj->madv == MSM_MADV_DONTNEED) && msm_obj->sgt &&
> !msm_obj->base.dma_buf && !msm_obj->base.import_attach;
> @@ -197,27 +205,12 @@ static inline bool is_purgeable(struct msm_gem_object *msm_obj)
>
> static inline bool is_vunmapable(struct msm_gem_object *msm_obj)
> {
> + WARN_ON(!msm_gem_is_locked(&msm_obj->base));
> return (msm_obj->vmap_count == 0) && msm_obj->vaddr;
> }
>
> -/* The shrinker can be triggered while we hold objA->lock, and need
> - * to grab objB->lock to purge it. Lockdep just sees these as a single
> - * class of lock, so we use subclasses to teach it the difference.
> - *
> - * OBJ_LOCK_NORMAL is implicit (ie. normal mutex_lock() call), and
> - * OBJ_LOCK_SHRINKER is used by shrinker.
> - *
> - * It is *essential* that we never go down paths that could trigger the
> - * shrinker for a purgable object. This is ensured by checking that
> - * msm_obj->madv == MSM_MADV_WILLNEED.
> - */
> -enum msm_gem_lock {
> - OBJ_LOCK_NORMAL,
> - OBJ_LOCK_SHRINKER,
> -};
> -
> -void msm_gem_purge(struct drm_gem_object *obj, enum msm_gem_lock subclass);
> -void msm_gem_vunmap(struct drm_gem_object *obj, enum msm_gem_lock subclass);
> +void msm_gem_purge(struct drm_gem_object *obj);
> +void msm_gem_vunmap(struct drm_gem_object *obj);
> void msm_gem_free_work(struct work_struct *work);
>
> /* Created per submit-ioctl, to track bo's and cmdstream bufs, etc,
> diff --git a/drivers/gpu/drm/msm/msm_gem_shrinker.c b/drivers/gpu/drm/msm/msm_gem_shrinker.c
> index 482576d7a39a..2dc0ffa925b4 100644
> --- a/drivers/gpu/drm/msm/msm_gem_shrinker.c
> +++ b/drivers/gpu/drm/msm/msm_gem_shrinker.c
> @@ -52,8 +52,11 @@ msm_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
> return 0;
>
> list_for_each_entry(msm_obj, &priv->inactive_list, mm_list) {
> + if (!msm_gem_trylock(&msm_obj->base))
> + continue;
> if (is_purgeable(msm_obj))
> count += msm_obj->base.size >> PAGE_SHIFT;
> + msm_gem_unlock(&msm_obj->base);
> }
>
> if (unlock)
> @@ -78,10 +81,13 @@ msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
> list_for_each_entry(msm_obj, &priv->inactive_list, mm_list) {
> if (freed >= sc->nr_to_scan)
> break;
> + if (!msm_gem_trylock(&msm_obj->base))
> + continue;
> if (is_purgeable(msm_obj)) {
> - msm_gem_purge(&msm_obj->base, OBJ_LOCK_SHRINKER);
> + msm_gem_purge(&msm_obj->base);
> freed += msm_obj->base.size >> PAGE_SHIFT;
> }
> + msm_gem_unlock(&msm_obj->base);
> }
>
> if (unlock)
> @@ -107,15 +113,20 @@ msm_gem_shrinker_vmap(struct notifier_block *nb, unsigned long event, void *ptr)
> return NOTIFY_DONE;
>
> list_for_each_entry(msm_obj, &priv->inactive_list, mm_list) {
> + if (!msm_gem_trylock(&msm_obj->base))
> + continue;
> if (is_vunmapable(msm_obj)) {
> - msm_gem_vunmap(&msm_obj->base, OBJ_LOCK_SHRINKER);
> - /* since we don't know any better, lets bail after a few
> - * and if necessary the shrinker will be invoked again.
> - * Seems better than unmapping *everything*
> - */
> - if (++unmapped >= 15)
> - break;
> + msm_gem_vunmap(&msm_obj->base);
> + unmapped++;
> }
> + msm_gem_unlock(&msm_obj->base);
> +
> + /* since we don't know any better, lets bail after a few
> + * and if necessary the shrinker will be invoked again.
> + * Seems better than unmapping *everything*
> + */
> + if (++unmapped >= 15)
> + break;
> }
>
> if (unlock)
> --
> 2.26.2
>
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