[PATCH v4 06/23] drm/msm/gem: Move locking in shrinker path

Rob Clark
2020-10-23T16:50:44Z

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>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
---
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..766ce278c74a 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(&msm_obj->lock) == 1;
+}
+
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