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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Wed, 14 Aug 2019 16:38:43 +0200
Subject: [PATCH] dma-buf: Use seqlock_t instread disabling preemption
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.4/older/patches-5.4.3-rt1.tar.xz
"dma reservation" disables preemption while acquiring the write access
for "seqcount".
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>
---
drivers/dma-buf/dma-buf.c | 8 ++--
drivers/dma-buf/dma-resv.c | 45 ++++++++---------------
drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c | 6 +--
drivers/gpu/drm/i915/gem/i915_gem_busy.c | 6 +--
include/linux/dma-resv.h | 4 +-
5 files changed, 27 insertions(+), 42 deletions(-)
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -214,7 +214,7 @@ static __poll_t dma_buf_poll(struct file
return 0;
retry:
- seq = read_seqcount_begin(&resv->seq);
+ seq = read_seqbegin(&resv->seq);
rcu_read_lock();
fobj = rcu_dereference(resv->fence);
@@ -223,7 +223,7 @@ static __poll_t dma_buf_poll(struct file
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;
}
@@ -1189,12 +1189,12 @@ static int dma_buf_debug_show(struct seq
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();
}
--- a/drivers/dma-buf/dma-resv.c
+++ b/drivers/dma-buf/dma-resv.c
@@ -49,12 +49,6 @@
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
@@ -103,8 +97,7 @@ 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);
+ seqlock_init(&obj->seq);
RCU_INIT_POINTER(obj->fence, NULL);
RCU_INIT_POINTER(obj->fence_excl, NULL);
}
@@ -234,8 +227,7 @@ void dma_resv_add_shared_fence(struct dm
fobj = dma_resv_get_list(obj);
count = fobj->shared_count;
- preempt_disable();
- write_seqcount_begin(&obj->seq);
+ write_seqlock(&obj->seq);
for (i = 0; i < count; ++i) {
@@ -255,8 +247,7 @@ void dma_resv_add_shared_fence(struct dm
/* 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();
+ write_sequnlock(&obj->seq);
dma_fence_put(old);
}
EXPORT_SYMBOL(dma_resv_add_shared_fence);
@@ -283,14 +274,12 @@ void dma_resv_add_excl_fence(struct dma_
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);
+ /* write_seqlock provides the necessary memory barrier */
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--)
@@ -368,13 +357,11 @@ int dma_resv_copy_fences(struct dma_resv
src_list = dma_resv_get_list(dst);
old = dma_resv_get_excl(dst);
- preempt_disable();
- write_seqcount_begin(&dst->seq);
- /* write_seqcount_begin provides the necessary memory barrier */
+ write_seqlock(&dst->seq);
+ /* write_seqlock 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();
+ write_sequnlock(&dst->seq);
dma_resv_list_free(src_list);
dma_fence_put(old);
@@ -414,7 +401,7 @@ int dma_resv_get_fences_rcu(struct dma_r
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))
@@ -456,7 +443,7 @@ int dma_resv_get_fences_rcu(struct dma_r
}
}
- 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);
@@ -507,7 +494,7 @@ long dma_resv_wait_timeout_rcu(struct dm
retry:
shared_count = 0;
- seq = read_seqcount_begin(&obj->seq);
+ seq = read_seqbegin(&obj->seq);
rcu_read_lock();
i = -1;
@@ -553,7 +540,7 @@ long dma_resv_wait_timeout_rcu(struct dm
rcu_read_unlock();
if (fence) {
- if (read_seqcount_retry(&obj->seq, seq)) {
+ if (read_seqretry(&obj->seq, seq)) {
dma_fence_put(fence);
goto retry;
}
@@ -607,7 +594,7 @@ bool dma_resv_test_signaled_rcu(struct d
retry:
ret = true;
shared_count = 0;
- seq = read_seqcount_begin(&obj->seq);
+ seq = read_seqbegin(&obj->seq);
if (test_all) {
unsigned i;
@@ -627,7 +614,7 @@ bool dma_resv_test_signaled_rcu(struct d
break;
}
- if (read_seqcount_retry(&obj->seq, seq))
+ if (read_seqretry(&obj->seq, seq))
goto retry;
}
@@ -639,7 +626,7 @@ bool dma_resv_test_signaled_rcu(struct d
if (ret < 0)
goto retry;
- if (read_seqcount_retry(&obj->seq, seq))
+ if (read_seqretry(&obj->seq, seq))
goto retry;
}
}
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
@@ -252,11 +252,9 @@ static int amdgpu_amdkfd_remove_eviction
new->shared_count = k;
/* 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) {
--- a/drivers/gpu/drm/i915/gem/i915_gem_busy.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_busy.c
@@ -75,7 +75,6 @@ busy_check_writer(const struct dma_fence
return __busy_set_if_active(fence, __busy_write_id);
}
-
int
i915_gem_busy_ioctl(struct drm_device *dev, void *data,
struct drm_file *file)
@@ -110,7 +109,8 @@ i915_gem_busy_ioctl(struct drm_device *d
*
*/
retry:
- seq = raw_read_seqcount(&obj->base.resv->seq);
+ /* XXX raw_read_seqcount() does not wait for the WRTIE to finish */
+ seq = read_seqbegin(&obj->base.resv->seq);
/* Translate the exclusive fence to the READ *and* WRITE engine */
args->busy =
@@ -129,7 +129,7 @@ i915_gem_busy_ioctl(struct drm_device *d
}
}
- if (args->busy && read_seqcount_retry(&obj->base.resv->seq, seq))
+ if (args->busy && read_seqretry(&obj->base.resv->seq, seq))
goto retry;
err = 0;
--- a/include/linux/dma-resv.h
+++ b/include/linux/dma-resv.h
@@ -65,13 +65,13 @@ struct dma_resv_list {
/**
* struct dma_resv - a reservation object manages fences for a buffer
* @lock: update side lock
- * @seq: sequence count for managing RCU read-side synchronization
+ * @seq: sequence lock for managing RCU read-side synchronization
* @fence_excl: the exclusive fence, if there is one currently
* @fence: list of current shared fences
*/
struct dma_resv {
struct ww_mutex lock;
- seqcount_t seq;
+ seqlock_t seq;
struct dma_fence __rcu *fence_excl;
struct dma_resv_list __rcu *fence;
|
