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dma-buf: Restore seqlock around dma_resv updates

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This reverts
67c97fb79a ("dma-buf: add reservation_object_fences helper")
dd7a7d1ff2 ("drm/i915: use new reservation_object_fences helper")
0e1d8083bd ("dma-buf: further relax reservation_object_add_shared_fence")
5d344f58da ("dma-buf: nuke reservation_object seq number")

The scenario that defeats simply grabbing a set of shared/exclusive
fences and using them blissfully under RCU is that any of those fences
may be reallocated by a SLAB_TYPESAFE_BY_RCU fence slab cache. In this
scenario, while keeping the rcu_read_lock we need to establish that no
fence was changed in the dma_resv after a read (or full) memory barrier.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190814182401.25009-1-chris@chris-wilson.co.uk
This commit is contained in:
Chris Wilson
2019-08-14 19:24:01 +01:00
parent dc2e1e5b27
commit b016cd6ed4
5 changed files with 175 additions and 109 deletions
Download Patch File Download Diff File Expand all files Collapse all files

109
drivers/dma-buf/dma-resv.c
View File

@@ -49,6 +49,12 @@
DEFINE_WD_CLASS(reservation_ww_class);
EXPORT_SYMBOL(reservation_ww_class);
struct lock_class_key reservation_seqcount_class;
EXPORT_SYMBOL(reservation_seqcount_class);
const char reservation_seqcount_string[] = "reservation_seqcount";
EXPORT_SYMBOL(reservation_seqcount_string);
/**
* dma_resv_list_alloc - allocate fence list
* @shared_max: number of fences we need space for
@@ -96,6 +102,9 @@ 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_init(&obj->seq, reservation_seqcount_string,
&reservation_seqcount_class);
RCU_INIT_POINTER(obj->fence, NULL);
RCU_INIT_POINTER(obj->fence_excl, NULL);
}
@@ -225,6 +234,9 @@ void dma_resv_add_shared_fence(struct dma_resv *obj, struct dma_fence *fence)
fobj = dma_resv_get_list(obj);
count = fobj->shared_count;
preempt_disable();
write_seqcount_begin(&obj->seq);
for (i = 0; i < count; ++i) {
old = rcu_dereference_protected(fobj->shared[i],
@@ -242,6 +254,9 @@ replace:
RCU_INIT_POINTER(fobj->shared[i], fence);
/* pointer update must be visible before we extend the shared_count */
smp_store_mb(fobj->shared_count, count);
write_seqcount_end(&obj->seq);
preempt_enable();
dma_fence_put(old);
}
EXPORT_SYMBOL(dma_resv_add_shared_fence);
@@ -269,10 +284,12 @@ void dma_resv_add_excl_fence(struct dma_resv *obj, struct dma_fence *fence)
dma_fence_get(fence);
preempt_disable();
rcu_assign_pointer(obj->fence_excl, fence);
/* pointer update must be visible before we modify the shared_count */
write_seqcount_begin(&obj->seq);
/* write_seqcount_begin provides the necessary memory barrier */
RCU_INIT_POINTER(obj->fence_excl, fence);
if (old)
smp_store_mb(old->shared_count, 0);
old->shared_count = 0;
write_seqcount_end(&obj->seq);
preempt_enable();
/* inplace update, no shared fences */
@@ -295,15 +312,17 @@ int dma_resv_copy_fences(struct dma_resv *dst, struct dma_resv *src)
{
struct dma_resv_list *src_list, *dst_list;
struct dma_fence *old, *new;
unsigned int i, shared_count;
unsigned i;
dma_resv_assert_held(dst);
rcu_read_lock();
src_list = rcu_dereference(src->fence);
retry:
dma_resv_fences(src, &new, &src_list, &shared_count);
if (shared_count) {
if (src_list) {
unsigned shared_count = src_list->shared_count;
rcu_read_unlock();
dst_list = dma_resv_list_alloc(shared_count);
@@ -311,14 +330,14 @@ retry:
return -ENOMEM;
rcu_read_lock();
dma_resv_fences(src, &new, &src_list, &shared_count);
if (!src_list || shared_count > dst_list->shared_max) {
src_list = rcu_dereference(src->fence);
if (!src_list || src_list->shared_count > shared_count) {
kfree(dst_list);
goto retry;
}
dst_list->shared_count = 0;
for (i = 0; i < shared_count; ++i) {
for (i = 0; i < src_list->shared_count; ++i) {
struct dma_fence *fence;
fence = rcu_dereference(src_list->shared[i]);
@@ -328,6 +347,7 @@ retry:
if (!dma_fence_get_rcu(fence)) {
dma_resv_list_free(dst_list);
src_list = rcu_dereference(src->fence);
goto retry;
}
@@ -342,18 +362,18 @@ retry:
dst_list = NULL;
}
if (new && !dma_fence_get_rcu(new)) {
dma_resv_list_free(dst_list);
goto retry;
}
new = dma_fence_get_rcu_safe(&src->fence_excl);
rcu_read_unlock();
src_list = dma_resv_get_list(dst);
old = dma_resv_get_excl(dst);
preempt_disable();
rcu_assign_pointer(dst->fence_excl, new);
rcu_assign_pointer(dst->fence, dst_list);
write_seqcount_begin(&dst->seq);
/* write_seqcount_begin provides the necessary memory barrier */
RCU_INIT_POINTER(dst->fence_excl, new);
RCU_INIT_POINTER(dst->fence, dst_list);
write_seqcount_end(&dst->seq);
preempt_enable();
dma_resv_list_free(src_list);
@@ -388,18 +408,19 @@ int dma_resv_get_fences_rcu(struct dma_resv *obj,
do {
struct dma_resv_list *fobj;
unsigned int i;
unsigned int i, seq;
size_t sz = 0;
i = 0;
shared_count = i = 0;
rcu_read_lock();
dma_resv_fences(obj, &fence_excl, &fobj,
&shared_count);
seq = read_seqcount_begin(&obj->seq);
fence_excl = rcu_dereference(obj->fence_excl);
if (fence_excl && !dma_fence_get_rcu(fence_excl))
goto unlock;
fobj = rcu_dereference(obj->fence);
if (fobj)
sz += sizeof(*shared) * fobj->shared_max;
@@ -427,6 +448,7 @@ int dma_resv_get_fences_rcu(struct dma_resv *obj,
break;
}
shared = nshared;
shared_count = fobj ? fobj->shared_count : 0;
for (i = 0; i < shared_count; ++i) {
shared[i] = rcu_dereference(fobj->shared[i]);
if (!dma_fence_get_rcu(shared[i]))
@@ -434,7 +456,7 @@ int dma_resv_get_fences_rcu(struct dma_resv *obj,
}
}
if (i != shared_count) {
if (i != shared_count || read_seqcount_retry(&obj->seq, seq)) {
while (i--)
dma_fence_put(shared[i]);
dma_fence_put(fence_excl);
@@ -478,17 +500,18 @@ long dma_resv_wait_timeout_rcu(struct dma_resv *obj,
bool wait_all, bool intr,
unsigned long timeout)
{
struct dma_resv_list *fobj;
struct dma_fence *fence;
unsigned shared_count;
unsigned seq, shared_count;
long ret = timeout ? timeout : 1;
int i;
retry:
shared_count = 0;
seq = read_seqcount_begin(&obj->seq);
rcu_read_lock();
i = -1;
dma_resv_fences(obj, &fence, &fobj, &shared_count);
fence = rcu_dereference(obj->fence_excl);
if (fence && !test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
if (!dma_fence_get_rcu(fence))
goto unlock_retry;
@@ -503,6 +526,11 @@ retry:
}
if (wait_all) {
struct dma_resv_list *fobj = rcu_dereference(obj->fence);
if (fobj)
shared_count = fobj->shared_count;
for (i = 0; !fence && i < shared_count; ++i) {
struct dma_fence *lfence = rcu_dereference(fobj->shared[i]);
@@ -525,6 +553,11 @@ retry:
rcu_read_unlock();
if (fence) {
if (read_seqcount_retry(&obj->seq, seq)) {
dma_fence_put(fence);
goto retry;
}
ret = dma_fence_wait_timeout(fence, intr, ret);
dma_fence_put(fence);
if (ret > 0 && wait_all && (i + 1 < shared_count))
@@ -567,19 +600,23 @@ static inline int dma_resv_test_signaled_single(struct dma_fence *passed_fence)
*/
bool dma_resv_test_signaled_rcu(struct dma_resv *obj, bool test_all)
{
struct dma_resv_list *fobj;
struct dma_fence *fence_excl;
unsigned shared_count;
unsigned seq, shared_count;
int ret;
rcu_read_lock();
retry:
ret = true;
shared_count = 0;
seq = read_seqcount_begin(&obj->seq);
dma_resv_fences(obj, &fence_excl, &fobj, &shared_count);
if (test_all) {
unsigned i;
struct dma_resv_list *fobj = rcu_dereference(obj->fence);
if (fobj)
shared_count = fobj->shared_count;
for (i = 0; i < shared_count; ++i) {
struct dma_fence *fence = rcu_dereference(fobj->shared[i]);
@@ -589,12 +626,22 @@ retry:
else if (!ret)
break;
}
if (read_seqcount_retry(&obj->seq, seq))
goto retry;
}
if (!shared_count && fence_excl) {
ret = dma_resv_test_signaled_single(fence_excl);
if (ret < 0)
goto retry;
if (!shared_count) {
struct dma_fence *fence_excl = rcu_dereference(obj->fence_excl);
if (fence_excl) {
ret = dma_resv_test_signaled_single(fence_excl);
if (ret < 0)
goto retry;
if (read_seqcount_retry(&obj->seq, seq))
goto retry;
}
}
rcu_read_unlock();