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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

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);