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dma-buf: drop seq count based update 

This should be possible now since we don't have the distinction
between exclusive and shared fences any more.

The only possible pitfall is that a dma_fence would be reused during the
RCU grace period, but even that could be handled with a single extra check.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220407085946.744568-15-christian.koenig@amd.com
This commit is contained in:
Christian König 2022-04-04 14:58:37 +02:00
parent 8bb3158782
commit 8f94eda399
3 changed files with 13 additions and 34 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

33
drivers/dma-buf/dma-resv.c
View File

@ -133,7 +133,6 @@ static void dma_resv_list_free(struct dma_resv_list *list)
void dma_resv_init(struct dma_resv *obj)
{
ww_mutex_init(&obj->lock, &reservation_ww_class);
seqcount_ww_mutex_init(&obj->seq, &obj->lock);
RCU_INIT_POINTER(obj->fences, NULL);
}
@ -292,28 +291,24 @@ void dma_resv_add_fence(struct dma_resv *obj, struct dma_fence *fence,
fobj = dma_resv_fences_list(obj);
count = fobj->num_fences;
write_seqcount_begin(&obj->seq);
for (i = 0; i < count; ++i) {
enum dma_resv_usage old_usage;
dma_resv_list_entry(fobj, i, obj, &old, &old_usage);
if ((old->context == fence->context && old_usage >= usage) ||
dma_fence_is_signaled(old))
goto replace;
dma_fence_is_signaled(old)) {
dma_resv_list_set(fobj, i, fence, usage);
dma_fence_put(old);
return;
}
}
BUG_ON(fobj->num_fences >= fobj->max_fences);
old = NULL;
count++;
replace:
dma_resv_list_set(fobj, i, fence, usage);
/* pointer update must be visible before we extend the num_fences */
smp_store_mb(fobj->num_fences, count);
write_seqcount_end(&obj->seq);
dma_fence_put(old);
}
EXPORT_SYMBOL(dma_resv_add_fence);
@ -341,7 +336,6 @@ void dma_resv_replace_fences(struct dma_resv *obj, uint64_t context,
dma_resv_assert_held(obj);
list = dma_resv_fences_list(obj);
write_seqcount_begin(&obj->seq);
for (i = 0; list && i < list->num_fences; ++i) {
struct dma_fence *old;
@ -352,14 +346,12 @@ void dma_resv_replace_fences(struct dma_resv *obj, uint64_t context,
dma_resv_list_set(list, i, replacement, usage);
dma_fence_put(old);
}
write_seqcount_end(&obj->seq);
}
EXPORT_SYMBOL(dma_resv_replace_fences);
/* Restart the unlocked iteration by initializing the cursor object. */
static void dma_resv_iter_restart_unlocked(struct dma_resv_iter *cursor)
{
cursor->seq = read_seqcount_begin(&cursor->obj->seq);
cursor->index = 0;
cursor->num_fences = 0;
cursor->fences = dma_resv_fences_list(cursor->obj);
@ -388,8 +380,10 @@ static void dma_resv_iter_walk_unlocked(struct dma_resv_iter *cursor)
cursor->obj, &cursor->fence,
&cursor->fence_usage);
cursor->fence = dma_fence_get_rcu(cursor->fence);
if (!cursor->fence)
break;
if (!cursor->fence) {
dma_resv_iter_restart_unlocked(cursor);
continue;
}
if (!dma_fence_is_signaled(cursor->fence) &&
cursor->usage >= cursor->fence_usage)
@ -415,7 +409,7 @@ struct dma_fence *dma_resv_iter_first_unlocked(struct dma_resv_iter *cursor)
do {
dma_resv_iter_restart_unlocked(cursor);
dma_resv_iter_walk_unlocked(cursor);
} while (read_seqcount_retry(&cursor->obj->seq, cursor->seq));
} while (dma_resv_fences_list(cursor->obj) != cursor->fences);
rcu_read_unlock();
return cursor->fence;
@ -438,13 +432,13 @@ struct dma_fence *dma_resv_iter_next_unlocked(struct dma_resv_iter *cursor)
rcu_read_lock();
cursor->is_restarted = false;
restart = read_seqcount_retry(&cursor->obj->seq, cursor->seq);
restart = dma_resv_fences_list(cursor->obj) != cursor->fences;
do {
if (restart)
dma_resv_iter_restart_unlocked(cursor);
dma_resv_iter_walk_unlocked(cursor);
restart = true;
} while (read_seqcount_retry(&cursor->obj->seq, cursor->seq));
} while (dma_resv_fences_list(cursor->obj) != cursor->fences);
rcu_read_unlock();
return cursor->fence;
@ -540,10 +534,7 @@ int dma_resv_copy_fences(struct dma_resv *dst, struct dma_resv *src)
}
dma_resv_iter_end(&cursor);
write_seqcount_begin(&dst->seq);
list = rcu_replace_pointer(dst->fences, list, dma_resv_held(dst));
write_seqcount_end(&dst->seq);
dma_resv_list_free(list);
return 0;
}

2
drivers/dma-buf/st-dma-resv.c
View File

@ -217,7 +217,7 @@ static int test_for_each_unlocked(void *arg)
if (r == -ENOENT) {
r = -EINVAL;
/* That should trigger an restart */
cursor.seq--;
cursor.fences = (void*)~0;
} else if (r == -EINVAL) {
r = 0;
}

12
include/linux/dma-resv.h
View File

@ -155,15 +155,6 @@ struct dma_resv {
*/
struct ww_mutex lock;
/**
* @seq:
*
* Sequence count for managing RCU read-side synchronization, allows
* read-only access to @fences while ensuring we take a consistent
* snapshot.
*/
seqcount_ww_mutex_t seq;
/**
* @fences:
*
@ -202,9 +193,6 @@ struct dma_resv_iter {
/** @fence_usage: the usage of the current fence */
enum dma_resv_usage fence_usage;
/** @seq: sequence number to check for modifications */
unsigned int seq;
/** @index: index into the shared fences */
unsigned int index;