Re: [RFC PATCH v1 08/16] drm/radeon: use common fence implementation for fences

Christian König
2014-05-14T15:29:32Z

> + /* did fence get signaled after we enabled the sw irq? */
> + if (atomic64_read(&fence->rdev->fence_drv[fence->ring].last_seq) >= fence->seq) {
> + radeon_irq_kms_sw_irq_put(fence->rdev, fence->ring);
> + return false;
> + }
> +
> + fence->fence_wake.flags = 0;
> + fence->fence_wake.private = NULL;
> + fence->fence_wake.func = radeon_fence_check_signaled;
> + __add_wait_queue(&fence->rdev->fence_queue, &fence->fence_wake);
> + fence_get(f);
That looks like a race condition to me. The fence needs to be added to
the wait queue before the check, not after.

Apart from that the whole approach looks like a really bad idea to me.
How for example is lockup detection supposed to happen with this?

Christian.

Am 14.05.2014 16:58, schrieb Maarten Lankhorst:
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
> ---
> drivers/gpu/drm/radeon/radeon.h | 15 +--
> drivers/gpu/drm/radeon/radeon_device.c | 1
> drivers/gpu/drm/radeon/radeon_fence.c | 189 +++++++++++++++++++++++++-------
> 3 files changed, 153 insertions(+), 52 deletions(-)
>
> diff --git a/drivers/gpu/drm/radeon/radeon.h b/drivers/gpu/drm/radeon/radeon.h
> index 68528619834a..a7d839a158ae 100644
> --- a/drivers/gpu/drm/radeon/radeon.h
> +++ b/drivers/gpu/drm/radeon/radeon.h
> @@ -64,6 +64,7 @@
> #include <linux/wait.h>
> #include <linux/list.h>
> #include <linux/kref.h>
> +#include <linux/fence.h>
>
> #include <ttm/ttm_bo_api.h>
> #include <ttm/ttm_bo_driver.h>
> @@ -113,9 +114,6 @@ extern int radeon_hard_reset;
> #define RADEONFB_CONN_LIMIT 4
> #define RADEON_BIOS_NUM_SCRATCH 8
>
> -/* fence seq are set to this number when signaled */
> -#define RADEON_FENCE_SIGNALED_SEQ 0LL
> -
> /* internal ring indices */
> /* r1xx+ has gfx CP ring */
> #define RADEON_RING_TYPE_GFX_INDEX 0
> @@ -347,12 +345,15 @@ struct radeon_fence_driver {
> };
>
> struct radeon_fence {
> + struct fence base;
> +
> struct radeon_device *rdev;
> - struct kref kref;
> /* protected by radeon_fence.lock */
> uint64_t seq;
> /* RB, DMA, etc. */
> unsigned ring;
> +
> + wait_queue_t fence_wake;
> };
>
> int radeon_fence_driver_start_ring(struct radeon_device *rdev, int ring);
> @@ -2256,6 +2257,7 @@ struct radeon_device {
> struct radeon_mman mman;
> struct radeon_fence_driver fence_drv[RADEON_NUM_RINGS];
> wait_queue_head_t fence_queue;
> + unsigned fence_context;
> struct mutex ring_lock;
> struct radeon_ring ring[RADEON_NUM_RINGS];
> bool ib_pool_ready;
> @@ -2346,11 +2348,6 @@ u32 cik_mm_rdoorbell(struct radeon_device *rdev, u32 index);
> void cik_mm_wdoorbell(struct radeon_device *rdev, u32 index, u32 v);
>
> /*
> - * Cast helper
> - */
> -#define to_radeon_fence(p) ((struct radeon_fence *)(p))
> -
> -/*
> * Registers read & write functions.
> */
> #define RREG8(reg) readb((rdev->rmmio) + (reg))
> diff --git a/drivers/gpu/drm/radeon/radeon_device.c b/drivers/gpu/drm/radeon/radeon_device.c
> index 0e770bbf7e29..501d0cf9eb8b 100644
> --- a/drivers/gpu/drm/radeon/radeon_device.c
> +++ b/drivers/gpu/drm/radeon/radeon_device.c
> @@ -1175,6 +1175,7 @@ int radeon_device_init(struct radeon_device *rdev,
> for (i = 0; i < RADEON_NUM_RINGS; i++) {
> rdev->ring[i].idx = i;
> }
> + rdev->fence_context = fence_context_alloc(RADEON_NUM_RINGS);
>
> DRM_INFO("initializing kernel modesetting (%s 0x%04X:0x%04X 0x%04X:0x%04X).\n",
> radeon_family_name[rdev->family], pdev->vendor, pdev->device,
> diff --git a/drivers/gpu/drm/radeon/radeon_fence.c b/drivers/gpu/drm/radeon/radeon_fence.c
> index a77b1c13ea43..bc844f300d3f 100644
> --- a/drivers/gpu/drm/radeon/radeon_fence.c
> +++ b/drivers/gpu/drm/radeon/radeon_fence.c
> @@ -39,6 +39,15 @@
> #include "radeon.h"
> #include "radeon_trace.h"
>
> +static const struct fence_ops radeon_fence_ops;
> +
> +#define to_radeon_fence(p) \
> + ({ \
> + struct radeon_fence *__f; \
> + __f = container_of((p), struct radeon_fence, base); \
> + __f->base.ops == &radeon_fence_ops ? __f : NULL; \
> + })
> +
> /*
> * Fences
> * Fences mark an event in the GPUs pipeline and are used
> @@ -111,30 +120,55 @@ int radeon_fence_emit(struct radeon_device *rdev,
> struct radeon_fence **fence,
> int ring)
> {
> + u64 seq = ++rdev->fence_drv[ring].sync_seq[ring];
> +
> /* we are protected by the ring emission mutex */
> *fence = kmalloc(sizeof(struct radeon_fence), GFP_KERNEL);
> if ((*fence) == NULL) {
> return -ENOMEM;
> }
> - kref_init(&((*fence)->kref));
> - (*fence)->rdev = rdev;
> - (*fence)->seq = ++rdev->fence_drv[ring].sync_seq[ring];
> (*fence)->ring = ring;
> + __fence_init(&(*fence)->base, &radeon_fence_ops,
> + &rdev->fence_queue.lock, rdev->fence_context + ring, seq);
> + (*fence)->rdev = rdev;
> + (*fence)->seq = seq;
> radeon_fence_ring_emit(rdev, ring, *fence);
> trace_radeon_fence_emit(rdev->ddev, ring, (*fence)->seq);
> return 0;
> }
>
> /**
> - * radeon_fence_process - process a fence
> + * radeon_fence_check_signaled - callback from fence_queue
> *
> - * @rdev: radeon_device pointer
> - * @ring: ring index the fence is associated with
> - *
> - * Checks the current fence value and wakes the fence queue
> - * if the sequence number has increased (all asics).
> + * this function is called with fence_queue lock held, which is also used
> + * for the fence locking itself, so unlocked variants are used for
> + * fence_signal, and remove_wait_queue.
> */
> -void radeon_fence_process(struct radeon_device *rdev, int ring)
> +static int radeon_fence_check_signaled(wait_queue_t *wait, unsigned mode, int flags, void *key)
> +{
> + struct radeon_fence *fence;
> + u64 seq;
> +
> + fence = container_of(wait, struct radeon_fence, fence_wake);
> +
> + seq = atomic64_read(&fence->rdev->fence_drv[fence->ring].last_seq);
> + if (seq >= fence->seq) {
> + int ret = __fence_signal(&fence->base);
> +
> + if (!ret)
> + FENCE_TRACE(&fence->base, "signaled from irq context\n");
> + else
> + FENCE_TRACE(&fence->base, "was already signaled\n");
> +
> + radeon_irq_kms_sw_irq_put(fence->rdev, fence->ring);
> + __remove_wait_queue(&fence->rdev->fence_queue, &fence->fence_wake);
> + fence_put(&fence->base);
> + } else
> + FENCE_TRACE(&fence->base, "pending\n");
> + return 0;
> +}
> +
> +static bool __radeon_fence_process(struct radeon_device *rdev, int ring)
> {
> uint64_t seq, last_seq, last_emitted;
> unsigned count_loop = 0;
> @@ -190,23 +224,22 @@ void radeon_fence_process(struct radeon_device *rdev, int ring)
> }
> } while (atomic64_xchg(&rdev->fence_drv[ring].last_seq, seq) > seq);
>
> - if (wake)
> - wake_up_all(&rdev->fence_queue);
> + return wake;
> }
>
> /**
> - * radeon_fence_destroy - destroy a fence
> + * radeon_fence_process - process a fence
> *
> - * @kref: fence kref
> + * @rdev: radeon_device pointer
> + * @ring: ring index the fence is associated with
> *
> - * Frees the fence object (all asics).
> + * Checks the current fence value and wakes the fence queue
> + * if the sequence number has increased (all asics).
> */
> -static void radeon_fence_destroy(struct kref *kref)
> +void radeon_fence_process(struct radeon_device *rdev, int ring)
> {
> - struct radeon_fence *fence;
> -
> - fence = container_of(kref, struct radeon_fence, kref);
> - kfree(fence);
> + if (__radeon_fence_process(rdev, ring))
> + wake_up_all(&rdev->fence_queue);
> }
>
> /**
> @@ -237,6 +270,49 @@ static bool radeon_fence_seq_signaled(struct radeon_device *rdev,
> return false;
> }
>
> +static bool __radeon_fence_signaled(struct fence *f)
> +{
> + struct radeon_fence *fence = to_radeon_fence(f);
> +
> + return radeon_fence_seq_signaled(fence->rdev, fence->seq, fence->ring);
> +}
> +
> +/**
> + * radeon_fence_enable_signaling - enable signalling on fence
> + * @fence: fence
> + *
> + * This function is called with fence_queue lock held, and adds a callback
> + * to fence_queue that checks if this fence is signaled, and if so it
> + * signals the fence and removes itself.
> + */
> +static bool radeon_fence_enable_signaling(struct fence *f)
> +{
> + struct radeon_fence *fence = to_radeon_fence(f);
> +
> + if (atomic64_read(&fence->rdev->fence_drv[fence->ring].last_seq) >= fence->seq ||
> + !fence->rdev->ddev->irq_enabled)
> + return false;
> +
> + radeon_irq_kms_sw_irq_get(fence->rdev, fence->ring);
> +
> + if (__radeon_fence_process(fence->rdev, fence->ring))
> + wake_up_all_locked(&fence->rdev->fence_queue);
> +
> + /* did fence get signaled after we enabled the sw irq? */
> + if (atomic64_read(&fence->rdev->fence_drv[fence->ring].last_seq) >= fence->seq) {
> + radeon_irq_kms_sw_irq_put(fence->rdev, fence->ring);
> + return false;
> + }
> +
> + fence->fence_wake.flags = 0;
> + fence->fence_wake.private = NULL;
> + fence->fence_wake.func = radeon_fence_check_signaled;
> + __add_wait_queue(&fence->rdev->fence_queue, &fence->fence_wake);
> + fence_get(f);
> +
> + return true;
> +}
> +
> /**
> * radeon_fence_signaled - check if a fence has signaled
> *
> @@ -250,11 +326,13 @@ bool radeon_fence_signaled(struct radeon_fence *fence)
> if (!fence) {
> return true;
> }
> - if (fence->seq == RADEON_FENCE_SIGNALED_SEQ) {
> - return true;
> - }
> +
> if (radeon_fence_seq_signaled(fence->rdev, fence->seq, fence->ring)) {
> - fence->seq = RADEON_FENCE_SIGNALED_SEQ;
> + int ret;
> +
> + ret = fence_signal(&fence->base);
> + if (!ret)
> + FENCE_TRACE(&fence->base, "signaled from radeon_fence_signaled\n");
> return true;
> }
> return false;
> @@ -386,7 +464,7 @@ static int radeon_fence_wait_seq(struct radeon_device *rdev, u64 *target_seq,
> * radeon_fence_wait - wait for a fence to signal
> *
> * @fence: radeon fence object
> - * @intr: use interruptable sleep
> + * @intr: use interruptible sleep
> *
> * Wait for the requested fence to signal (all asics).
> * @intr selects whether to use interruptable (true) or non-interruptable
> @@ -398,20 +476,17 @@ int radeon_fence_wait(struct radeon_fence *fence, bool intr)
> uint64_t seq[RADEON_NUM_RINGS] = {};
> int r;
>
> - if (fence == NULL) {
> - WARN(1, "Querying an invalid fence : %p !\n", fence);
> - return -EINVAL;
> - }
> -
> - seq[fence->ring] = fence->seq;
> - if (seq[fence->ring] == RADEON_FENCE_SIGNALED_SEQ)
> + if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fence->base.flags))
> return 0;
>
> + seq[fence->ring] = fence->seq;
> r = radeon_fence_wait_seq(fence->rdev, seq, intr);
> - if (r)
> + if (r) {
> return r;
> -
> - fence->seq = RADEON_FENCE_SIGNALED_SEQ;
> + }
> + r = fence_signal(&fence->base);
> + if (!r)
> + FENCE_TRACE(&fence->base, "signaled from fence_wait\n");
> return 0;
> }
>
> @@ -443,12 +518,13 @@ int radeon_fence_wait_any(struct radeon_device *rdev,
> continue;
> }
>
> + if (test_bit(FENCE_FLAG_SIGNALED_BIT, &fences[i]->base.flags)) {
> + /* already signaled */
> + return 0;
> + }
> +
> seq[i] = fences[i]->seq;
> ++num_rings;
> -
> - /* test if something was allready signaled */
> - if (seq[i] == RADEON_FENCE_SIGNALED_SEQ)
> - return 0;
> }
>
> /* nothing to wait for ? */
> @@ -525,7 +601,7 @@ int radeon_fence_wait_empty(struct radeon_device *rdev, int ring)
> */
> struct radeon_fence *radeon_fence_ref(struct radeon_fence *fence)
> {
> - kref_get(&fence->kref);
> + fence_get(&fence->base);
> return fence;
> }
>
> @@ -541,9 +617,8 @@ void radeon_fence_unref(struct radeon_fence **fence)
> struct radeon_fence *tmp = *fence;
>
> *fence = NULL;
> - if (tmp) {
> - kref_put(&tmp->kref, radeon_fence_destroy);
> - }
> + if (tmp)
> + fence_put(&tmp->base);
> }
>
> /**
> @@ -832,3 +907,31 @@ int radeon_debugfs_fence_init(struct radeon_device *rdev)
> return 0;
> #endif
> }
> +
> +static const char *radeon_fence_get_driver_name(struct fence *fence)
> +{
> + return "radeon";
> +}
> +
> +static const char *radeon_fence_get_timeline_name(struct fence *f)
> +{
> + struct radeon_fence *fence = to_radeon_fence(f);
> + switch (fence->ring) {
> + case RADEON_RING_TYPE_GFX_INDEX: return "radeon.gfx";
> + case CAYMAN_RING_TYPE_CP1_INDEX: return "radeon.cp1";
> + case CAYMAN_RING_TYPE_CP2_INDEX: return "radeon.cp2";
> + case R600_RING_TYPE_DMA_INDEX: return "radeon.dma";
> + case CAYMAN_RING_TYPE_DMA1_INDEX: return "radeon.dma1";
> + case R600_RING_TYPE_UVD_INDEX: return "radeon.uvd";
> + default: WARN_ON_ONCE(1); return "radeon.unk";
> + }
> +}
> +
> +static const struct fence_ops radeon_fence_ops = {
> + .get_driver_name = radeon_fence_get_driver_name,
> + .get_timeline_name = radeon_fence_get_timeline_name,
> + .enable_signaling = radeon_fence_enable_signaling,
> + .signaled = __radeon_fence_signaled,
> + .wait = fence_default_wait,
> + .release = NULL,
> +};
>
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