[PATCH 5.10 634/717] drm/panfrost: Move the GPU reset bits outside the timeout handler

Greg Kroah-Hartman
2020-12-28T14:30:01Z

From: Boris Brezillon <boris.brezillon@collabora.com>

commit 5bc5cc2819c2c0adb644919e3e790b504ea47e0a upstream.

We've fixed many races in panfrost_job_timedout() but some remain.
Instead of trying to fix it again, let's simplify the logic and move
the reset bits to a separate work scheduled when one of the queue
reports a timeout.

v5:
- Simplify panfrost_scheduler_stop() (Steven Price)
- Always restart the queue in panfrost_scheduler_start() even if
the status is corrupted (Steven Price)

v4:
- Rework the logic to prevent a race between drm_sched_start()
(reset work) and drm_sched_job_timedout() (timeout work)
- Drop Steven's R-b
- Add dma_fence annotation to the panfrost_reset() function (Daniel Vetter)

v3:
- Replace the atomic_cmpxchg() by an atomic_xchg() (Robin Murphy)
- Add Steven's R-b

v2:
- Use atomic_cmpxchg() to conditionally schedule the reset work
(Steven Price)

Fixes: 1a11a88cfd9a ("drm/panfrost: Fix job timeout handling")
Cc: <stable@vger.kernel.org>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201105151704.2010667-1-boris.brezillon@collabora.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/gpu/drm/panfrost/panfrost_device.c | 1
drivers/gpu/drm/panfrost/panfrost_device.h | 6
drivers/gpu/drm/panfrost/panfrost_job.c | 187 +++++++++++++++++++----------
3 files changed, 130 insertions(+), 64 deletions(-)

--- a/drivers/gpu/drm/panfrost/panfrost_device.c
+++ b/drivers/gpu/drm/panfrost/panfrost_device.c
@@ -206,7 +206,6 @@ int panfrost_device_init(struct panfrost
struct resource *res;

mutex_init(&pfdev->sched_lock);
- mutex_init(&pfdev->reset_lock);
INIT_LIST_HEAD(&pfdev->scheduled_jobs);
INIT_LIST_HEAD(&pfdev->as_lru_list);

--- a/drivers/gpu/drm/panfrost/panfrost_device.h
+++ b/drivers/gpu/drm/panfrost/panfrost_device.h
@@ -105,7 +105,11 @@ struct panfrost_device {
struct panfrost_perfcnt *perfcnt;

struct mutex sched_lock;
- struct mutex reset_lock;
+
+ struct {
+ struct work_struct work;
+ atomic_t pending;
+ } reset;

struct mutex shrinker_lock;
struct list_head shrinker_list;
--- a/drivers/gpu/drm/panfrost/panfrost_job.c
+++ b/drivers/gpu/drm/panfrost/panfrost_job.c
@@ -20,12 +20,21 @@
#include "panfrost_gpu.h"
#include "panfrost_mmu.h"

+#define JOB_TIMEOUT_MS 500
+
#define job_write(dev, reg, data) writel(data, dev->iomem + (reg))
#define job_read(dev, reg) readl(dev->iomem + (reg))

+enum panfrost_queue_status {
+ PANFROST_QUEUE_STATUS_ACTIVE,
+ PANFROST_QUEUE_STATUS_STOPPED,
+ PANFROST_QUEUE_STATUS_STARTING,
+ PANFROST_QUEUE_STATUS_FAULT_PENDING,
+};
+
struct panfrost_queue_state {
struct drm_gpu_scheduler sched;
- bool stopped;
+ atomic_t status;
struct mutex lock;
u64 fence_context;
u64 emit_seqno;
@@ -373,28 +382,61 @@ void panfrost_job_enable_interrupts(stru
static bool panfrost_scheduler_stop(struct panfrost_queue_state *queue,
struct drm_sched_job *bad)
{
+ enum panfrost_queue_status old_status;
bool stopped = false;

mutex_lock(&queue->lock);
- if (!queue->stopped) {
- drm_sched_stop(&queue->sched, bad);
- if (bad)
- drm_sched_increase_karma(bad);
- queue->stopped = true;
- stopped = true;
- }
+ old_status = atomic_xchg(&queue->status,
+ PANFROST_QUEUE_STATUS_STOPPED);
+ if (old_status == PANFROST_QUEUE_STATUS_STOPPED)
+ goto out;
+
+ WARN_ON(old_status != PANFROST_QUEUE_STATUS_ACTIVE);
+ drm_sched_stop(&queue->sched, bad);
+ if (bad)
+ drm_sched_increase_karma(bad);
+
+ stopped = true;
+
+ /*
+ * Set the timeout to max so the timer doesn't get started
+ * when we return from the timeout handler (restored in
+ * panfrost_scheduler_start()).
+ */
+ queue->sched.timeout = MAX_SCHEDULE_TIMEOUT;
+
+out:
mutex_unlock(&queue->lock);

return stopped;
}

+static void panfrost_scheduler_start(struct panfrost_queue_state *queue)
+{
+ enum panfrost_queue_status old_status;
+
+ mutex_lock(&queue->lock);
+ old_status = atomic_xchg(&queue->status,
+ PANFROST_QUEUE_STATUS_STARTING);
+ WARN_ON(old_status != PANFROST_QUEUE_STATUS_STOPPED);
+
+ /* Restore the original timeout before starting the scheduler. */
+ queue->sched.timeout = msecs_to_jiffies(JOB_TIMEOUT_MS);
+ drm_sched_resubmit_jobs(&queue->sched);
+ drm_sched_start(&queue->sched, true);
+ old_status = atomic_xchg(&queue->status,
+ PANFROST_QUEUE_STATUS_ACTIVE);
+ if (old_status == PANFROST_QUEUE_STATUS_FAULT_PENDING)
+ drm_sched_fault(&queue->sched);
+
+ mutex_unlock(&queue->lock);
+}
+
static void panfrost_job_timedout(struct drm_sched_job *sched_job)
{
struct panfrost_job *job = to_panfrost_job(sched_job);
struct panfrost_device *pfdev = job->pfdev;
int js = panfrost_job_get_slot(job);
- unsigned long flags;
- int i;

/*
* If the GPU managed to complete this jobs fence, the timeout is
@@ -415,56 +457,9 @@ static void panfrost_job_timedout(struct
if (!panfrost_scheduler_stop(&pfdev->js->queue[js], sched_job))
return;

- if (!mutex_trylock(&pfdev->reset_lock))
- return;
-
- for (i = 0; i < NUM_JOB_SLOTS; i++) {
- struct drm_gpu_scheduler *sched = &pfdev->js->queue[i].sched;
-
- /*
- * If the queue is still active, make sure we wait for any
- * pending timeouts.
- */
- if (!pfdev->js->queue[i].stopped)
- cancel_delayed_work_sync(&sched->work_tdr);
-
- /*
- * If the scheduler was not already stopped, there's a tiny
- * chance a timeout has expired just before we stopped it, and
- * drm_sched_stop() does not flush pending works. Let's flush
- * them now so the timeout handler doesn't get called in the
- * middle of a reset.
- */
- if (panfrost_scheduler_stop(&pfdev->js->queue[i], NULL))
- cancel_delayed_work_sync(&sched->work_tdr);
-
- /*
- * Now that we cancelled the pending timeouts, we can safely
- * reset the stopped state.
- */
- pfdev->js->queue[i].stopped = false;
- }
-
- spin_lock_irqsave(&pfdev->js->job_lock, flags);
- for (i = 0; i < NUM_JOB_SLOTS; i++) {
- if (pfdev->jobs[i]) {
- pm_runtime_put_noidle(pfdev->dev);
- panfrost_devfreq_record_idle(&pfdev->pfdevfreq);
- pfdev->jobs[i] = NULL;
- }
- }
- spin_unlock_irqrestore(&pfdev->js->job_lock, flags);
-
- panfrost_device_reset(pfdev);
-
- for (i = 0; i < NUM_JOB_SLOTS; i++)
- drm_sched_resubmit_jobs(&pfdev->js->queue[i].sched);
-
- mutex_unlock(&pfdev->reset_lock);
-
- /* restart scheduler after GPU is usable again */
- for (i = 0; i < NUM_JOB_SLOTS; i++)
- drm_sched_start(&pfdev->js->queue[i].sched, true);
+ /* Schedule a reset if there's no reset in progress. */
+ if (!atomic_xchg(&pfdev->reset.pending, 1))
+ schedule_work(&pfdev->reset.work);
}

static const struct drm_sched_backend_ops panfrost_sched_ops = {
@@ -496,6 +491,8 @@ static irqreturn_t panfrost_job_irq_hand
job_write(pfdev, JOB_INT_CLEAR, mask);

if (status & JOB_INT_MASK_ERR(j)) {
+ enum panfrost_queue_status old_status;
+
job_write(pfdev, JS_COMMAND_NEXT(j), JS_COMMAND_NOP);

dev_err(pfdev->dev, "js fault, js=%d, status=%s, head=0x%x, tail=0x%x",
@@ -504,7 +501,18 @@ static irqreturn_t panfrost_job_irq_hand
job_read(pfdev, JS_HEAD_LO(j)),
job_read(pfdev, JS_TAIL_LO(j)));

- drm_sched_fault(&pfdev->js->queue[j].sched);
+ /*
+ * When the queue is being restarted we don't report
+ * faults directly to avoid races between the timeout
+ * and reset handlers. panfrost_scheduler_start() will
+ * call drm_sched_fault() after the queue has been
+ * started if status == FAULT_PENDING.
+ */
+ old_status = atomic_cmpxchg(&pfdev->js->queue[j].status,
+ PANFROST_QUEUE_STATUS_STARTING,
+ PANFROST_QUEUE_STATUS_FAULT_PENDING);
+ if (old_status == PANFROST_QUEUE_STATUS_ACTIVE)
+ drm_sched_fault(&pfdev->js->queue[j].sched);
}

if (status & JOB_INT_MASK_DONE(j)) {
@@ -531,11 +539,66 @@ static irqreturn_t panfrost_job_irq_hand
return IRQ_HANDLED;
}

+static void panfrost_reset(struct work_struct *work)
+{
+ struct panfrost_device *pfdev = container_of(work,
+ struct panfrost_device,
+ reset.work);
+ unsigned long flags;
+ unsigned int i;
+ bool cookie;
+
+ cookie = dma_fence_begin_signalling();
+ for (i = 0; i < NUM_JOB_SLOTS; i++) {
+ /*
+ * We want pending timeouts to be handled before we attempt
+ * to stop the scheduler. If we don't do that and the timeout
+ * handler is in flight, it might have removed the bad job
+ * from the list, and we'll lose this job if the reset handler
+ * enters the critical section in panfrost_scheduler_stop()
+ * before the timeout handler.
+ *
+ * Timeout is set to MAX_SCHEDULE_TIMEOUT - 1 because we need
+ * something big enough to make sure the timer will not expire
+ * before we manage to stop the scheduler, but we can't use
+ * MAX_SCHEDULE_TIMEOUT because drm_sched_get_cleanup_job()
+ * considers that as 'timer is not running' and will dequeue
+ * the job without making sure the timeout handler is not
+ * running.
+ */
+ pfdev->js->queue[i].sched.timeout = MAX_SCHEDULE_TIMEOUT - 1;
+ cancel_delayed_work_sync(&pfdev->js->queue[i].sched.work_tdr);
+ panfrost_scheduler_stop(&pfdev->js->queue[i], NULL);
+ }
+
+ /* All timers have been stopped, we can safely reset the pending state. */
+ atomic_set(&pfdev->reset.pending, 0);
+
+ spin_lock_irqsave(&pfdev->js->job_lock, flags);
+ for (i = 0; i < NUM_JOB_SLOTS; i++) {
+ if (pfdev->jobs[i]) {
+ pm_runtime_put_noidle(pfdev->dev);
+ panfrost_devfreq_record_idle(&pfdev->pfdevfreq);
+ pfdev->jobs[i] = NULL;
+ }
+ }
+ spin_unlock_irqrestore(&pfdev->js->job_lock, flags);
+
+ panfrost_device_reset(pfdev);
+
+ for (i = 0; i < NUM_JOB_SLOTS; i++)
+ panfrost_scheduler_start(&pfdev->js->queue[i]);
+
+ dma_fence_end_signalling(cookie);
+}
+
int panfrost_job_init(struct panfrost_device *pfdev)
{
struct panfrost_job_slot *js;
int ret, j, irq;

+ INIT_WORK(&pfdev->reset.work, panfrost_reset);
+
pfdev->js = js = devm_kzalloc(pfdev->dev, sizeof(*js), GFP_KERNEL);
if (!js)
return -ENOMEM;
@@ -558,7 +621,7 @@ int panfrost_job_init(struct panfrost_de

ret = drm_sched_init(&js->queue[j].sched,
&panfrost_sched_ops,
- 1, 0, msecs_to_jiffies(500),
+ 1, 0, msecs_to_jiffies(JOB_TIMEOUT_MS),
"pan_js");
if (ret) {
dev_err(pfdev->dev, "Failed to create scheduler: %d.", ret);