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linux/dma-fence.h: Allow fences to be signaled after their refcount g…
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…oing down to zero

as long as their .release callback hasn't called dma_fence_free() yet. This
semantics is not documented anywhere, and is probably just an
implementation detail, but the vmwgfx driver heavily relies on it.

Sorry riastradh@, this is unfortunate but circumventing this (admittedly
healthy) assertion requires a major code reorganization of the driver. We
really can't fight against the upstream on this matter.
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@depressed-pho
depressed-pho committed Jul 15, 2023
1 parent 0a65674 commit af88505
Showing 1 changed file with 33 additions and 31 deletions.
64 changes: 33 additions & 31 deletions sys/external/bsd/drm2/linux/linux_dma_fence.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -146,6 +146,18 @@ linux_dma_fences_fini(void)
spin_lock_destroy(&dma_fence_stub.lock);
}

/*
* dma_fence_assert_alive(fence)
*
* Assert that fence hasn't been destroyed.
*/
static inline void __diagused
dma_fence_assert_alive(struct dma_fence *fence)
{
KASSERTMSG(fence->f_magic != FENCE_MAGIC_BAD, "fence %p", fence);
KASSERTMSG(fence->f_magic == FENCE_MAGIC_GOOD, "fence %p", fence);
}

/*
* dma_fence_referenced_p(fence)
*
Expand All @@ -158,8 +170,7 @@ static inline bool __diagused
dma_fence_referenced_p(struct dma_fence *fence)
{

KASSERTMSG(fence->f_magic != FENCE_MAGIC_BAD, "fence %p", fence);
KASSERTMSG(fence->f_magic == FENCE_MAGIC_GOOD, "fence %p", fence);
dma_fence_assert_alive(fence);

return kref_referenced_p(&fence->refcount);
}
Expand Down Expand Up @@ -206,8 +217,7 @@ dma_fence_reset(struct dma_fence *fence, const struct dma_fence_ops *ops,
spinlock_t *lock, uint64_t context, uint64_t seqno)
{

KASSERTMSG(fence->f_magic != FENCE_MAGIC_BAD, "fence %p", fence);
KASSERTMSG(fence->f_magic == FENCE_MAGIC_GOOD, "fence %p", fence);
dma_fence_assert_alive(fence);
KASSERT(kref_read(&fence->refcount) == 0 ||
kref_read(&fence->refcount) == 1);
KASSERT(TAILQ_EMPTY(&fence->f_callbacks));
Expand Down Expand Up @@ -345,10 +355,8 @@ bool
dma_fence_is_later(struct dma_fence *a, struct dma_fence *b)
{

KASSERTMSG(a->f_magic != FENCE_MAGIC_BAD, "fence %p", a);
KASSERTMSG(a->f_magic == FENCE_MAGIC_GOOD, "fence %p", a);
KASSERTMSG(b->f_magic != FENCE_MAGIC_BAD, "fence %p", b);
KASSERTMSG(b->f_magic == FENCE_MAGIC_GOOD, "fence %p", b);
dma_fence_assert_alive(a);
dma_fence_assert_alive(b);
KASSERTMSG(a->context == b->context, "incommensurate fences"
": %"PRIu64" @ %p =/= %"PRIu64" @ %p",
a->context, a, b->context, b);
Expand Down Expand Up @@ -382,8 +390,7 @@ dma_fence_get(struct dma_fence *fence)
if (fence == NULL)
return NULL;

KASSERTMSG(fence->f_magic != FENCE_MAGIC_BAD, "fence %p", fence);
KASSERTMSG(fence->f_magic == FENCE_MAGIC_GOOD, "fence %p", fence);
dma_fence_assert_alive(fence);

kref_get(&fence->refcount);
return fence;
Expand All @@ -401,8 +408,7 @@ dma_fence_get_rcu(struct dma_fence *fence)
{

__insn_barrier();
KASSERTMSG(fence->f_magic != FENCE_MAGIC_BAD, "fence %p", fence);
KASSERTMSG(fence->f_magic == FENCE_MAGIC_GOOD, "fence %p", fence);
dma_fence_assert_alive(fence);
if (!kref_get_unless_zero(&fence->refcount))
return NULL;
return fence;
Expand Down Expand Up @@ -498,7 +504,7 @@ dma_fence_ensure_signal_enabled(struct dma_fence *fence)
{
bool already_enabled;

KASSERT(dma_fence_referenced_p(fence));
dma_fence_assert_alive(fence);
KASSERT(spin_is_locked(fence->lock));

/* Determine whether signalling was enabled, and enable it. */
Expand Down Expand Up @@ -544,7 +550,7 @@ dma_fence_add_callback(struct dma_fence *fence, struct dma_fence_cb *fcb,
{
int ret;

KASSERT(dma_fence_referenced_p(fence));
dma_fence_assert_alive(fence);

/* Optimistically try to skip the lock if it's already signalled. */
if (atomic_load_relaxed(&fence->flags) &
Expand Down Expand Up @@ -590,7 +596,7 @@ dma_fence_remove_callback(struct dma_fence *fence, struct dma_fence_cb *fcb)
{
bool onqueue;

KASSERT(dma_fence_referenced_p(fence));
dma_fence_assert_alive(fence);

spin_lock(fence->lock);
onqueue = fcb->fcb_onqueue;
Expand All @@ -616,7 +622,7 @@ void
dma_fence_enable_sw_signaling(struct dma_fence *fence)
{

KASSERT(dma_fence_referenced_p(fence));
dma_fence_assert_alive(fence);

spin_lock(fence->lock);
if ((fence->flags & (1u << DMA_FENCE_FLAG_SIGNALED_BIT)) == 0)
Expand All @@ -638,7 +644,7 @@ dma_fence_is_signaled(struct dma_fence *fence)
{
bool signaled;

KASSERT(dma_fence_referenced_p(fence));
dma_fence_assert_alive(fence);

spin_lock(fence->lock);
signaled = dma_fence_is_signaled_locked(fence);
Expand All @@ -657,7 +663,7 @@ bool
dma_fence_is_signaled_locked(struct dma_fence *fence)
{

KASSERT(dma_fence_referenced_p(fence));
dma_fence_assert_alive(fence);
KASSERT(spin_is_locked(fence->lock));

/* Check whether we already set the signalled bit. */
Expand Down Expand Up @@ -691,8 +697,7 @@ void
dma_fence_set_error(struct dma_fence *fence, int error)
{

KASSERTMSG(fence->f_magic != FENCE_MAGIC_BAD, "fence %p", fence);
KASSERTMSG(fence->f_magic == FENCE_MAGIC_GOOD, "fence %p", fence);
dma_fence_assert_alive(fence);
KASSERT((atomic_load_relaxed(&fence->flags) &
(1u << DMA_FENCE_FLAG_SIGNALED_BIT)) == 0);
KASSERTMSG(error >= -ELAST, "%d", error);
Expand All @@ -714,8 +719,7 @@ dma_fence_get_status(struct dma_fence *fence)
{
int ret;

KASSERTMSG(fence->f_magic != FENCE_MAGIC_BAD, "fence %p", fence);
KASSERTMSG(fence->f_magic == FENCE_MAGIC_GOOD, "fence %p", fence);
dma_fence_assert_alive(fence);

spin_lock(fence->lock);
if (!dma_fence_is_signaled_locked(fence)) {
Expand Down Expand Up @@ -745,7 +749,7 @@ dma_fence_signal(struct dma_fence *fence)
{
int ret;

KASSERT(dma_fence_referenced_p(fence));
dma_fence_assert_alive(fence);

spin_lock(fence->lock);
ret = dma_fence_signal_locked(fence);
Expand All @@ -765,7 +769,7 @@ dma_fence_signal_locked(struct dma_fence *fence)
{
struct dma_fence_cb *fcb, *next;

KASSERT(dma_fence_referenced_p(fence));
dma_fence_assert_alive(fence);
KASSERT(spin_is_locked(fence->lock));

/* If it's been signalled, fail; otherwise set the signalled bit. */
Expand Down Expand Up @@ -808,7 +812,7 @@ wait_any_cb(struct dma_fence *fence, struct dma_fence_cb *fcb)
{
struct wait_any *cb = container_of(fcb, struct wait_any, fcb);

KASSERT(dma_fence_referenced_p(fence));
dma_fence_assert_alive(fence);

mutex_enter(&cb->common->lock);
cb->common->done = true;
Expand Down Expand Up @@ -841,7 +845,7 @@ dma_fence_wait_any_timeout(struct dma_fence **fences, uint32_t nfences,

/* Optimistically check whether any are signalled. */
for (i = 0; i < nfences; i++) {
KASSERT(dma_fence_referenced_p(fences[i]));
dma_fence_assert_alive(fences[i]);
if (dma_fence_is_signaled(fences[i])) {
if (ip)
*ip = i;
Expand Down Expand Up @@ -873,7 +877,7 @@ dma_fence_wait_any_timeout(struct dma_fence **fences, uint32_t nfences,
*/
for (i = 0; i < nfences; i++) {
cb[i].common = &common;
KASSERT(dma_fence_referenced_p(fences[i]));
dma_fence_assert_alive(fences[i]);
ret = dma_fence_add_callback(fences[i], &cb[i].fcb,
&wait_any_cb);
if (ret) {
Expand Down Expand Up @@ -1158,8 +1162,7 @@ bool
__dma_fence_signal(struct dma_fence *fence)
{

KASSERTMSG(fence->f_magic != FENCE_MAGIC_BAD, "fence %p", fence);
KASSERTMSG(fence->f_magic == FENCE_MAGIC_GOOD, "fence %p", fence);
dma_fence_assert_alive(fence);

if (test_and_set_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
return false;
Expand All @@ -1179,8 +1182,7 @@ __dma_fence_signal_wake(struct dma_fence *fence, ktime_t timestamp)
{
struct dma_fence_cb *fcb, *next;

KASSERTMSG(fence->f_magic != FENCE_MAGIC_BAD, "fence %p", fence);
KASSERTMSG(fence->f_magic == FENCE_MAGIC_GOOD, "fence %p", fence);
dma_fence_assert_alive(fence);

spin_lock(fence->lock);

Expand Down

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