[PATCH RT 05/32] dma-buf: Use seqlock_t instread disabling preemption

Steven Rostedt
2020-01-17T17:43:08Z

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

[ Upstream commit 240610aa31094f51f299f06eb8dae8d4cd8d4500 ]

"dma reservation" disables preemption while acquiring the write access
for "seqcount" and then may acquire a spinlock_t.

Replace the seqcount with a seqlock_t which provides seqcount like
semantic and lock for writer.

Link: https://lkml.kernel.org/r/f410b429-db86-f81c-7c67-f563fa808b62@free.fr
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
drivers/dma-buf/dma-buf.c | 8 ++--
drivers/dma-buf/reservation.c | 43 +++++++------------
.../gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c | 6 +--
drivers/gpu/drm/i915/i915_gem.c | 10 ++---
include/linux/reservation.h | 4 +-
5 files changed, 29 insertions(+), 42 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 69842145c223..4c3ef46e7149 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -179,7 +179,7 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
return 0;

retry:
- seq = read_seqcount_begin(&resv->seq);
+ seq = read_seqbegin(&resv->seq);
rcu_read_lock();

fobj = rcu_dereference(resv->fence);
@@ -188,7 +188,7 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
else
shared_count = 0;
fence_excl = rcu_dereference(resv->fence_excl);
- if (read_seqcount_retry(&resv->seq, seq)) {
+ if (read_seqretry(&resv->seq, seq)) {
rcu_read_unlock();
goto retry;
}
@@ -1046,12 +1046,12 @@ static int dma_buf_debug_show(struct seq_file *s, void *unused)

robj = buf_obj->resv;
while (true) {
- seq = read_seqcount_begin(&robj->seq);
+ seq = read_seqbegin(&robj->seq);
rcu_read_lock();
fobj = rcu_dereference(robj->fence);
shared_count = fobj ? fobj->shared_count : 0;
fence = rcu_dereference(robj->fence_excl);
- if (!read_seqcount_retry(&robj->seq, seq))
+ if (!read_seqretry(&robj->seq, seq))
break;
rcu_read_unlock();
}
diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c
index 49ab09468ba1..f11d58492216 100644
--- a/drivers/dma-buf/reservation.c
+++ b/drivers/dma-buf/reservation.c
@@ -109,8 +109,7 @@ reservation_object_add_shared_inplace(struct reservation_object *obj,

dma_fence_get(fence);

- preempt_disable();
- write_seqcount_begin(&obj->seq);
+ write_seqlock(&obj->seq);

for (i = 0; i < fobj->shared_count; ++i) {
struct dma_fence *old_fence;
@@ -121,8 +120,7 @@ reservation_object_add_shared_inplace(struct reservation_object *obj,
if (old_fence->context == fence->context) {
/* memory barrier is added by write_seqcount_begin */
RCU_INIT_POINTER(fobj->shared[i], fence);
- write_seqcount_end(&obj->seq);
- preempt_enable();
+ write_sequnlock(&obj->seq);

dma_fence_put(old_fence);
return;
@@ -146,8 +144,7 @@ reservation_object_add_shared_inplace(struct reservation_object *obj,
fobj->shared_count++;
}

- write_seqcount_end(&obj->seq);
- preempt_enable();
+ write_sequnlock(&obj->seq);

dma_fence_put(signaled);
}
@@ -191,15 +188,13 @@ reservation_object_add_shared_replace(struct reservation_object *obj,
fobj->shared_count++;

done:
- preempt_disable();
- write_seqcount_begin(&obj->seq);
+ write_seqlock(&obj->seq);
/*
* RCU_INIT_POINTER can be used here,
* seqcount provides the necessary barriers
*/
RCU_INIT_POINTER(obj->fence, fobj);
- write_seqcount_end(&obj->seq);
- preempt_enable();
+ write_sequnlock(&obj->seq);

if (!old)
return;
@@ -259,14 +254,11 @@ void reservation_object_add_excl_fence(struct reservation_object *obj,
if (fence)
dma_fence_get(fence);

- preempt_disable();
- write_seqcount_begin(&obj->seq);
- /* write_seqcount_begin provides the necessary memory barrier */
+ write_seqlock(&obj->seq);
RCU_INIT_POINTER(obj->fence_excl, fence);
if (old)
old->shared_count = 0;
- write_seqcount_end(&obj->seq);
- preempt_enable();
+ write_sequnlock(&obj->seq);

/* inplace update, no shared fences */
while (i--)
@@ -349,13 +341,10 @@ int reservation_object_copy_fences(struct reservation_object *dst,
src_list = reservation_object_get_list(dst);
old = reservation_object_get_excl(dst);

- preempt_disable();
- write_seqcount_begin(&dst->seq);
- /* write_seqcount_begin provides the necessary memory barrier */
+ write_seqlock(&dst->seq);
RCU_INIT_POINTER(dst->fence_excl, new);
RCU_INIT_POINTER(dst->fence, dst_list);
- write_seqcount_end(&dst->seq);
- preempt_enable();
+ write_sequnlock(&dst->seq);

if (src_list)
kfree_rcu(src_list, rcu);
@@ -396,7 +385,7 @@ int reservation_object_get_fences_rcu(struct reservation_object *obj,
shared_count = i = 0;

rcu_read_lock();
- seq = read_seqcount_begin(&obj->seq);
+ seq = read_seqbegin(&obj->seq);

fence_excl = rcu_dereference(obj->fence_excl);
if (fence_excl && !dma_fence_get_rcu(fence_excl))
@@ -445,7 +434,7 @@ int reservation_object_get_fences_rcu(struct reservation_object *obj,
}
}

- if (i != shared_count || read_seqcount_retry(&obj->seq, seq)) {
+ if (i != shared_count || read_seqretry(&obj->seq, seq)) {
while (i--)
dma_fence_put(shared[i]);
dma_fence_put(fence_excl);
@@ -494,7 +483,7 @@ long reservation_object_wait_timeout_rcu(struct reservation_object *obj,

retry:
shared_count = 0;
- seq = read_seqcount_begin(&obj->seq);
+ seq = read_seqbegin(&obj->seq);
rcu_read_lock();
i = -1;

@@ -541,7 +530,7 @@ long reservation_object_wait_timeout_rcu(struct reservation_object *obj,

rcu_read_unlock();
if (fence) {
- if (read_seqcount_retry(&obj->seq, seq)) {
+ if (read_seqretry(&obj->seq, seq)) {
dma_fence_put(fence);
goto retry;
}
@@ -597,7 +586,7 @@ bool reservation_object_test_signaled_rcu(struct reservation_object *obj,
retry:
ret = true;
shared_count = 0;
- seq = read_seqcount_begin(&obj->seq);
+ seq = read_seqbegin(&obj->seq);

if (test_all) {
unsigned i;
@@ -618,7 +607,7 @@ bool reservation_object_test_signaled_rcu(struct reservation_object *obj,
break;
}

- if (read_seqcount_retry(&obj->seq, seq))
+ if (read_seqretry(&obj->seq, seq))
goto retry;
}

@@ -631,7 +620,7 @@ bool reservation_object_test_signaled_rcu(struct reservation_object *obj,
if (ret < 0)
goto retry;

- if (read_seqcount_retry(&obj->seq, seq))
+ if (read_seqretry(&obj->seq, seq))
goto retry;
}
}
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
index f92597c292fe..10c675850aac 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
@@ -261,11 +261,9 @@ static int amdgpu_amdkfd_remove_eviction_fence(struct amdgpu_bo *bo,
}

/* Install the new fence list, seqcount provides the barriers */
- preempt_disable();
- write_seqcount_begin(&resv->seq);
+ write_seqlock(&resv->seq);
RCU_INIT_POINTER(resv->fence, new);
- write_seqcount_end(&resv->seq);
- preempt_enable();
+ write_sequnlock(&resv->seq);

/* Drop the references to the removed fences or move them to ef_list */
for (i = j, k = 0; i < old->shared_count; ++i) {
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index c7d05ac7af3c..d484e79316bf 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -516,7 +516,7 @@ i915_gem_object_wait_reservation(struct reservation_object *resv,
long timeout,
struct intel_rps_client *rps_client)
{
- unsigned int seq = __read_seqcount_begin(&resv->seq);
+ unsigned int seq = read_seqbegin(&resv->seq);
struct dma_fence *excl;
bool prune_fences = false;

@@ -569,9 +569,9 @@ i915_gem_object_wait_reservation(struct reservation_object *resv,
* signaled and that the reservation object has not been changed (i.e.
* no new fences have been added).
*/
- if (prune_fences && !__read_seqcount_retry(&resv->seq, seq)) {
+ if (prune_fences && !read_seqretry(&resv->seq, seq)) {
if (reservation_object_trylock(resv)) {
- if (!__read_seqcount_retry(&resv->seq, seq))
+ if (!read_seqretry(&resv->seq, seq))
reservation_object_add_excl_fence(resv, NULL);
reservation_object_unlock(resv);
}
@@ -4615,7 +4615,7 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
*
*/
retry:
- seq = raw_read_seqcount(&obj->resv->seq);
+ seq = read_seqbegin(&obj->resv->seq);

/* Translate the exclusive fence to the READ *and* WRITE engine */
args->busy = busy_check_writer(rcu_dereference(obj->resv->fence_excl));
@@ -4633,7 +4633,7 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
}
}

- if (args->busy && read_seqcount_retry(&obj->resv->seq, seq))
+ if (args->busy && read_seqretry(&obj->resv->seq, seq))
goto retry;

err = 0;
diff --git a/include/linux/reservation.h b/include/linux/reservation.h
index 02166e815afb..0b31df1af698 100644
--- a/include/linux/reservation.h
+++ b/include/linux/reservation.h
@@ -72,7 +72,7 @@ struct reservation_object_list {
*/
struct reservation_object {
struct ww_mutex lock;
- seqcount_t seq;
+ seqlock_t seq;

struct dma_fence __rcu *fence_excl;
struct reservation_object_list __rcu *fence;
@@ -92,7 +92,7 @@ reservation_object_init(struct reservation_object *obj)
{
ww_mutex_init(&obj->lock, &reservation_ww_class);

- __seqcount_init(&obj->seq, reservation_seqcount_string, &reservation_seqcount_class);
+ seqlock_init(&obj->seq);
RCU_INIT_POINTER(obj->fence, NULL);
RCU_INIT_POINTER(obj->fence_excl, NULL);
obj->staged = NULL;
--
2.24.1