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dma-buf: Restore seqlock around dma_resv updates 

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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
drivers/dma-buf/dma-buf.c
View File

@ -199,7 +199,7 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
struct dma_resv_list *fobj;
struct dma_fence *fence_excl;
__poll_t events;
unsigned shared_count;
unsigned shared_count, seq;
dmabuf = file->private_data;
if (!dmabuf || !dmabuf->resv)
@ -213,8 +213,21 @@ static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
if (!events)
return 0;
retry:
seq = read_seqcount_begin(&resv->seq);
rcu_read_lock();
dma_resv_fences(resv, &fence_excl, &fobj, &shared_count);
fobj = rcu_dereference(resv->fence);
if (fobj)
shared_count = fobj->shared_count;
else
shared_count = 0;
fence_excl = rcu_dereference(resv->fence_excl);
if (read_seqcount_retry(&resv->seq, seq)) {
rcu_read_unlock();
goto retry;
}
if (fence_excl && (!(events & EPOLLOUT) || shared_count == 0)) {
struct dma_buf_poll_cb_t *dcb = &dmabuf->cb_excl;
__poll_t pevents = EPOLLIN;
@ -1144,6 +1157,7 @@ static int dma_buf_debug_show(struct seq_file *s, void *unused)
struct dma_resv *robj;
struct dma_resv_list *fobj;
struct dma_fence *fence;
unsigned seq;
int count = 0, attach_count, shared_count, i;
size_t size = 0;
@ -1174,9 +1188,16 @@ static int dma_buf_debug_show(struct seq_file *s, void *unused)
buf_obj->name ?: "");
robj = buf_obj->resv;
rcu_read_lock();
dma_resv_fences(robj, &fence, &fobj, &shared_count);
rcu_read_unlock();
while (true) {
seq = read_seqcount_begin(&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))
break;
rcu_read_unlock();
}
if (fence)
seq_printf(s, "\tExclusive fence: %s %s %ssignalled\n",

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();

7
drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
View File

@ -251,7 +251,12 @@ static int amdgpu_amdkfd_remove_eviction_fence(struct amdgpu_bo *bo,
new->shared_max = old->shared_max;
new->shared_count = k;
rcu_assign_pointer(resv->fence, new);
/* Install the new fence list, seqcount provides the barriers */
preempt_disable();
write_seqcount_begin(&resv->seq);
RCU_INIT_POINTER(resv->fence, new);
write_seqcount_end(&resv->seq);
preempt_enable();
/* Drop the references to the removed fences or move them to ef_list */
for (i = j, k = 0; i < old->shared_count; ++i) {

24
drivers/gpu/drm/i915/gem/i915_gem_busy.c
View File

@ -83,8 +83,7 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
struct drm_i915_gem_busy *args = data;
struct drm_i915_gem_object *obj;
struct dma_resv_list *list;
unsigned int i, shared_count;
struct dma_fence *excl;
unsigned int seq;
int err;
err = -ENOENT;
@ -110,18 +109,29 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
* to report the overall busyness. This is what the wait-ioctl does.
*
*/
dma_resv_fences(obj->base.resv, &excl, &list, &shared_count);
retry:
seq = raw_read_seqcount(&obj->base.resv->seq);
/* Translate the exclusive fence to the READ *and* WRITE engine */
args->busy = busy_check_writer(excl);
args->busy =
busy_check_writer(rcu_dereference(obj->base.resv->fence_excl));
/* Translate shared fences to READ set of engines */
for (i = 0; i < shared_count; ++i) {
struct dma_fence *fence = rcu_dereference(list->shared[i]);
list = rcu_dereference(obj->base.resv->fence);
if (list) {
unsigned int shared_count = list->shared_count, i;
args->busy |= busy_check_reader(fence);
for (i = 0; i < shared_count; ++i) {
struct dma_fence *fence =
rcu_dereference(list->shared[i]);
args->busy |= busy_check_reader(fence);
}
}
if (args->busy && read_seqcount_retry(&obj->base.resv->seq, seq))
goto retry;
err = 0;
out:
rcu_read_unlock();

113
include/linux/dma-resv.h
View File

@ -46,6 +46,8 @@
#include <linux/rcupdate.h>
extern struct ww_class reservation_ww_class;
extern struct lock_class_key reservation_seqcount_class;
extern const char reservation_seqcount_string[];
/**
* struct dma_resv_list - a list of shared fences
@ -69,6 +71,7 @@ struct dma_resv_list {
*/
struct dma_resv {
struct ww_mutex lock;
seqcount_t seq;
struct dma_fence __rcu *fence_excl;
struct dma_resv_list __rcu *fence;
@ -77,24 +80,6 @@ struct dma_resv {
#define dma_resv_held(obj) lockdep_is_held(&(obj)->lock.base)
#define dma_resv_assert_held(obj) lockdep_assert_held(&(obj)->lock.base)
/**
* dma_resv_get_excl - get the reservation object's
* exclusive fence, with update-side lock held
* @obj: the reservation object
*
* Returns the exclusive fence (if any). Does NOT take a
* reference. Writers must hold obj->lock, readers may only
* hold a RCU read side lock.
*
* RETURNS
* The exclusive fence or NULL
*/
static inline struct dma_fence *dma_resv_get_excl(struct dma_resv *obj)
{
return rcu_dereference_protected(obj->fence_excl,
dma_resv_held(obj));
}
/**
* dma_resv_get_list - get the reservation object's
* shared fence list, with update-side lock held
@ -109,53 +94,6 @@ static inline struct dma_resv_list *dma_resv_get_list(struct dma_resv *obj)
dma_resv_held(obj));
}
/**
* dma_resv_fences - read consistent fence pointers
* @obj: reservation object where we get the fences from
* @excl: pointer for the exclusive fence
* @list: pointer for the shared fence list
*
* Make sure we have a consisten exclusive fence and shared fence list.
* Must be called with rcu read side lock held.
*/
static inline void dma_resv_fences(struct dma_resv *obj,
struct dma_fence **excl,
struct dma_resv_list **list,
u32 *shared_count)
{
do {
*excl = rcu_dereference(obj->fence_excl);
*list = rcu_dereference(obj->fence);
*shared_count = *list ? (*list)->shared_count : 0;
smp_rmb(); /* See dma_resv_add_excl_fence */
} while (rcu_access_pointer(obj->fence_excl) != *excl);
}
/**
* dma_resv_get_excl_rcu - get the reservation object's
* exclusive fence, without lock held.
* @obj: the reservation object
*
* If there is an exclusive fence, this atomically increments it's
* reference count and returns it.
*
* RETURNS
* The exclusive fence or NULL if none
*/
static inline struct dma_fence *dma_resv_get_excl_rcu(struct dma_resv *obj)
{
struct dma_fence *fence;
if (!rcu_access_pointer(obj->fence_excl))
return NULL;
rcu_read_lock();
fence = dma_fence_get_rcu_safe(&obj->fence_excl);
rcu_read_unlock();
return fence;
}
/**
* dma_resv_lock - lock the reservation object
* @obj: the reservation object
@ -290,6 +228,51 @@ static inline void dma_resv_unlock(struct dma_resv *obj)
ww_mutex_unlock(&obj->lock);
}
/**
* dma_resv_get_excl - get the reservation object's
* exclusive fence, with update-side lock held
* @obj: the reservation object
*
* Returns the exclusive fence (if any). Does NOT take a
* reference. Writers must hold obj->lock, readers may only
* hold a RCU read side lock.
*
* RETURNS
* The exclusive fence or NULL
*/
static inline struct dma_fence *
dma_resv_get_excl(struct dma_resv *obj)
{
return rcu_dereference_protected(obj->fence_excl,
dma_resv_held(obj));
}
/**
* dma_resv_get_excl_rcu - get the reservation object's
* exclusive fence, without lock held.
* @obj: the reservation object
*
* If there is an exclusive fence, this atomically increments it's
* reference count and returns it.
*
* RETURNS
* The exclusive fence or NULL if none
*/
static inline struct dma_fence *
dma_resv_get_excl_rcu(struct dma_resv *obj)
{
struct dma_fence *fence;
if (!rcu_access_pointer(obj->fence_excl))
return NULL;
rcu_read_lock();
fence = dma_fence_get_rcu_safe(&obj->fence_excl);
rcu_read_unlock();
return fence;
}
void dma_resv_init(struct dma_resv *obj);
void dma_resv_fini(struct dma_resv *obj);
int dma_resv_reserve_shared(struct dma_resv *obj, unsigned int num_fences);