Am 14.08.19 um 20:26 schrieb Chris Wilson: > Quoting Chris Wilson (2019-08-14 19:24:01) >> This reverts >> 67c97fb79a7f ("dma-buf: add reservation_object_fences helper") >> dd7a7d1ff2f1 ("drm/i915: use new reservation_object_fences helper") >> 0e1d8083bddb ("dma-buf: further relax reservation_object_add_shared_fence") >> 5d344f58da76 ("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@xxxxxxxxxxxxxxxxxx> Acked-by: Christian König <christian.koenig@xxxxxxx> >> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > I said I needed to go lie down, that proves it. > > Cc: Christian König <christian.koenig@xxxxxxx> > >> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx> >> --- >> drivers/dma-buf/dma-buf.c | 31 ++++- >> drivers/dma-buf/dma-resv.c | 109 ++++++++++++----- >> .../gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c | 7 +- >> drivers/gpu/drm/i915/gem/i915_gem_busy.c | 24 ++-- >> include/linux/dma-resv.h | 113 ++++++++---------- >> 5 files changed, 175 insertions(+), 109 deletions(-) >> >> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c >> index b3400d6524ab..433d91d710e4 100644 >> --- a/drivers/dma-buf/dma-buf.c >> +++ b/drivers/dma-buf/dma-buf.c >> @@ -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", >> diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c >> index f5142683c851..42a8f3f11681 100644 >> --- a/drivers/dma-buf/dma-resv.c >> +++ b/drivers/dma-buf/dma-resv.c >> @@ -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 @@ void dma_resv_add_shared_fence(struct dma_resv *obj, struct dma_fence *fence) >> 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 @@ int dma_resv_copy_fences(struct dma_resv *dst, struct dma_resv *src) >> 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 @@ int dma_resv_copy_fences(struct dma_resv *dst, struct dma_resv *src) >> >> if (!dma_fence_get_rcu(fence)) { >> dma_resv_list_free(dst_list); >> + src_list = rcu_dereference(src->fence); >> goto retry; >> } >> >> @@ -342,18 +362,18 @@ int dma_resv_copy_fences(struct dma_resv *dst, struct dma_resv *src) >> 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 @@ long dma_resv_wait_timeout_rcu(struct dma_resv *obj, >> } >> >> 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 @@ long dma_resv_wait_timeout_rcu(struct dma_resv *obj, >> >> 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]); >> >> @@ -589,14 +626,24 @@ bool dma_resv_test_signaled_rcu(struct dma_resv *obj, bool test_all) >> else if (!ret) >> break; >> } >> - } >> >> - if (!shared_count && fence_excl) { >> - ret = dma_resv_test_signaled_single(fence_excl); >> - if (ret < 0) >> + if (read_seqcount_retry(&obj->seq, seq)) >> 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(); >> return ret; >> } >> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c >> index bc4ec6b20a87..76e3516484e7 100644 >> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c >> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c >> @@ -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) { >> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_busy.c b/drivers/gpu/drm/i915/gem/i915_gem_busy.c >> index a2aff1d8290e..3d4f5775a4ba 100644 >> --- a/drivers/gpu/drm/i915/gem/i915_gem_busy.c >> +++ b/drivers/gpu/drm/i915/gem/i915_gem_busy.c >> @@ -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(); >> diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h >> index 38f2802afabb..ee50d10f052b 100644 >> --- a/include/linux/dma-resv.h >> +++ b/include/linux/dma-resv.h >> @@ -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); >> -- >> 2.23.0.rc1 >> _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel