[PATCH 1/6] drm/ttm: remove lru_lock around ttm_bo_reserve
Maarten Lankhorst
m.b.lankhorst at gmail.com
Fri Nov 30 04:12:55 PST 2012
There should no longer be assumptions that reserve will always succeed
with the lru lock held, so we can safely break the whole atomic
reserve/lru thing. As a bonus this fixes most lockdep annotations for
reservations.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst at canonical.com>
---
drivers/gpu/drm/ttm/ttm_bo.c | 54 ++++++++++++++++++++++------------
drivers/gpu/drm/ttm/ttm_execbuf_util.c | 2 +-
include/drm/ttm/ttm_bo_driver.h | 19 +++---------
3 files changed, 40 insertions(+), 35 deletions(-)
diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index 9028327..61b5cd0 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -213,14 +213,13 @@ int ttm_bo_del_from_lru(struct ttm_buffer_object *bo)
return put_count;
}
-int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
+int ttm_bo_reserve_nolru(struct ttm_buffer_object *bo,
bool interruptible,
bool no_wait, bool use_sequence, uint32_t sequence)
{
- struct ttm_bo_global *glob = bo->glob;
int ret;
- while (unlikely(atomic_read(&bo->reserved) != 0)) {
+ while (unlikely(atomic_xchg(&bo->reserved, 1) != 0)) {
/**
* Deadlock avoidance for multi-bo reserving.
*/
@@ -241,26 +240,36 @@ int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
if (no_wait)
return -EBUSY;
- spin_unlock(&glob->lru_lock);
ret = ttm_bo_wait_unreserved(bo, interruptible);
- spin_lock(&glob->lru_lock);
if (unlikely(ret))
return ret;
}
- atomic_set(&bo->reserved, 1);
if (use_sequence) {
+ bool wake_up = false;
/**
* Wake up waiters that may need to recheck for deadlock,
* if we decreased the sequence number.
*/
if (unlikely((bo->val_seq - sequence < (1 << 31))
|| !bo->seq_valid))
- wake_up_all(&bo->event_queue);
+ wake_up = true;
+ /*
+ * In the worst case with memory ordering these values can be
+ * seen in the wrong order. However since we call wake_up_all
+ * in that case, this will hopefully not pose a problem,
+ * and the worst case would only cause someone to accidentally
+ * hit -EAGAIN in ttm_bo_reserve when they see old value of
+ * val_seq. However this would only happen if seq_valid was
+ * written before val_seq was, and just means some slightly
+ * increased cpu usage
+ */
bo->val_seq = sequence;
bo->seq_valid = true;
+ if (wake_up)
+ wake_up_all(&bo->event_queue);
} else {
bo->seq_valid = false;
}
@@ -289,14 +298,14 @@ int ttm_bo_reserve(struct ttm_buffer_object *bo,
int put_count = 0;
int ret;
- spin_lock(&glob->lru_lock);
- ret = ttm_bo_reserve_locked(bo, interruptible, no_wait, use_sequence,
- sequence);
- if (likely(ret == 0))
+ ret = ttm_bo_reserve_nolru(bo, interruptible, no_wait, use_sequence,
+ sequence);
+ if (likely(ret == 0)) {
+ spin_lock(&glob->lru_lock);
put_count = ttm_bo_del_from_lru(bo);
- spin_unlock(&glob->lru_lock);
-
- ttm_bo_list_ref_sub(bo, put_count, true);
+ spin_unlock(&glob->lru_lock);
+ ttm_bo_list_ref_sub(bo, put_count, true);
+ }
return ret;
}
@@ -510,7 +519,7 @@ static void ttm_bo_cleanup_refs_or_queue(struct ttm_buffer_object *bo)
int ret;
spin_lock(&glob->lru_lock);
- ret = ttm_bo_reserve_locked(bo, false, true, false, 0);
+ ret = ttm_bo_reserve_nolru(bo, false, true, false, 0);
spin_lock(&bdev->fence_lock);
(void) ttm_bo_wait(bo, false, false, true);
@@ -603,7 +612,7 @@ static int ttm_bo_cleanup_refs_and_unlock(struct ttm_buffer_object *bo,
return ret;
spin_lock(&glob->lru_lock);
- ret = ttm_bo_reserve_locked(bo, false, true, false, 0);
+ ret = ttm_bo_reserve_nolru(bo, false, true, false, 0);
/*
* We raced, and lost, someone else holds the reservation now,
@@ -667,7 +676,14 @@ static int ttm_bo_delayed_delete(struct ttm_bo_device *bdev, bool remove_all)
kref_get(&nentry->list_kref);
}
- ret = ttm_bo_reserve_locked(entry, false, !remove_all, false, 0);
+ ret = ttm_bo_reserve_nolru(entry, false, true, false, 0);
+ if (remove_all && ret) {
+ spin_unlock(&glob->lru_lock);
+ ret = ttm_bo_reserve_nolru(entry, false, false,
+ false, 0);
+ spin_lock(&glob->lru_lock);
+ }
+
if (!ret)
ret = ttm_bo_cleanup_refs_and_unlock(entry, false,
!remove_all);
@@ -818,7 +834,7 @@ static int ttm_mem_evict_first(struct ttm_bo_device *bdev,
spin_lock(&glob->lru_lock);
list_for_each_entry(bo, &man->lru, lru) {
- ret = ttm_bo_reserve_locked(bo, false, true, false, 0);
+ ret = ttm_bo_reserve_nolru(bo, false, true, false, 0);
if (!ret)
break;
}
@@ -1799,7 +1815,7 @@ static int ttm_bo_swapout(struct ttm_mem_shrink *shrink)
spin_lock(&glob->lru_lock);
list_for_each_entry(bo, &glob->swap_lru, swap) {
- ret = ttm_bo_reserve_locked(bo, false, true, false, 0);
+ ret = ttm_bo_reserve_nolru(bo, false, true, false, 0);
if (!ret)
break;
}
diff --git a/drivers/gpu/drm/ttm/ttm_execbuf_util.c b/drivers/gpu/drm/ttm/ttm_execbuf_util.c
index cd9e452..bd37b5c 100644
--- a/drivers/gpu/drm/ttm/ttm_execbuf_util.c
+++ b/drivers/gpu/drm/ttm/ttm_execbuf_util.c
@@ -153,7 +153,7 @@ retry:
struct ttm_buffer_object *bo = entry->bo;
retry_this_bo:
- ret = ttm_bo_reserve_locked(bo, true, true, true, val_seq);
+ ret = ttm_bo_reserve_nolru(bo, true, true, true, val_seq);
switch (ret) {
case 0:
break;
diff --git a/include/drm/ttm/ttm_bo_driver.h b/include/drm/ttm/ttm_bo_driver.h
index e3a43a4..6fff432 100644
--- a/include/drm/ttm/ttm_bo_driver.h
+++ b/include/drm/ttm/ttm_bo_driver.h
@@ -790,16 +790,7 @@ extern void ttm_mem_io_unlock(struct ttm_mem_type_manager *man);
* to make room for a buffer already reserved. (Buffers are reserved before
* they are evicted). The following algorithm prevents such deadlocks from
* occurring:
- * 1) Buffers are reserved with the lru spinlock held. Upon successful
- * reservation they are removed from the lru list. This stops a reserved buffer
- * from being evicted. However the lru spinlock is released between the time
- * a buffer is selected for eviction and the time it is reserved.
- * Therefore a check is made when a buffer is reserved for eviction, that it
- * is still the first buffer in the lru list, before it is removed from the
- * list. @check_lru == 1 forces this check. If it fails, the function returns
- * -EINVAL, and the caller should then choose a new buffer to evict and repeat
- * the procedure.
- * 2) Processes attempting to reserve multiple buffers other than for eviction,
+ * Processes attempting to reserve multiple buffers other than for eviction,
* (typically execbuf), should first obtain a unique 32-bit
* validation sequence number,
* and call this function with @use_sequence == 1 and @sequence == the unique
@@ -832,7 +823,7 @@ extern int ttm_bo_reserve(struct ttm_buffer_object *bo,
/**
- * ttm_bo_reserve_locked:
+ * ttm_bo_reserve_nolru:
*
* @bo: A pointer to a struct ttm_buffer_object.
* @interruptible: Sleep interruptible if waiting.
@@ -840,9 +831,7 @@ extern int ttm_bo_reserve(struct ttm_buffer_object *bo,
* @use_sequence: If @bo is already reserved, Only sleep waiting for
* it to become unreserved if @sequence < (@bo)->sequence.
*
- * Must be called with struct ttm_bo_global::lru_lock held,
- * and will not remove reserved buffers from the lru lists.
- * The function may release the LRU spinlock if it needs to sleep.
+ * Will not remove reserved buffers from the lru lists.
* Otherwise identical to ttm_bo_reserve.
*
* Returns:
@@ -855,7 +844,7 @@ extern int ttm_bo_reserve(struct ttm_buffer_object *bo,
* -EDEADLK: Bo already reserved using @sequence. This error code will only
* be returned if @use_sequence is set to true.
*/
-extern int ttm_bo_reserve_locked(struct ttm_buffer_object *bo,
+extern int ttm_bo_reserve_nolru(struct ttm_buffer_object *bo,
bool interruptible,
bool no_wait, bool use_sequence,
uint32_t sequence);
--
1.8.0
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