Previously, we were able to rely on the recursive properties of
struct_mutex to allow us to serialise revoking mmaps and reacquiring the
FENCE registers with them being clobbered over a global device reset.
I then proceeded to throw out the baby with the bath water in order to
pursue a struct_mutex-less reset.
Perusing LWN for alternative strategies, the dilemma on how to serialise
access to a global resource on one side was answered by
https://lwn.net/Articles/202847/ -- Sleepable RCU:
1 int readside(void) {
2 int idx;
3 rcu_read_lock();
4 if (nomoresrcu) {
5 rcu_read_unlock();
6 return -EINVAL;
7 }
8 idx = srcu_read_lock(&ss);
9 rcu_read_unlock();
10 /* SRCU read-side critical section. */
11 srcu_read_unlock(&ss, idx);
12 return 0;
13 }
14
15 void cleanup(void)
16 {
17 nomoresrcu = 1;
18 synchronize_rcu();
19 synchronize_srcu(&ss);
20 cleanup_srcu_struct(&ss);
21 }
No more worrying about stop_machine, just an uber-complex mutex,
optimised for reads, with the overhead pushed to the rare reset path.
However, we do run the risk of a deadlock as we allocate underneath the
SRCU read lock, and the allocation may require a GPU reset, causing a
dependency cycle via the in-flight requests. We resolve that by declaring
the driver wedged and cancelling all in-flight rendering.
v2: Use expedited rcu barriers to match our earlier timing
characteristics.
v3: Try to annotate locking contexts for sparse
v4: Reduce selftest lock duration to avoid a reset deadlock with fences
v5: s/srcu/reset_backoff_srcu/
v6: Remove more stale comments
Testcase: igt/gem_mmap_gtt/hang
Fixes:
eb8d0f5af4ec ("drm/i915: Remove GPU reset dependence on struct_mutex")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190208153708.20023-2-chris@chris-wilson.co.uk
intel_wakeref_t wakeref;
enum intel_engine_id id;
+ seq_printf(m, "Reset flags: %lx\n", dev_priv->gpu_error.flags);
if (test_bit(I915_WEDGED, &dev_priv->gpu_error.flags))
- seq_puts(m, "Wedged\n");
+ seq_puts(m, "\tWedged\n");
if (test_bit(I915_RESET_BACKOFF, &dev_priv->gpu_error.flags))
- seq_puts(m, "Reset in progress: struct_mutex backoff\n");
- if (waitqueue_active(&dev_priv->gpu_error.wait_queue))
- seq_puts(m, "Waiter holding struct mutex\n");
- if (waitqueue_active(&dev_priv->gpu_error.reset_queue))
- seq_puts(m, "struct_mutex blocked for reset\n");
+ seq_puts(m, "\tDevice (global) reset in progress\n");
if (!i915_modparams.enable_hangcheck) {
seq_puts(m, "Hangcheck disabled\n");
* while it is writing to 'i915_wedged'
*/
- if (i915_reset_backoff(&i915->gpu_error))
- return -EAGAIN;
-
i915_handle_error(i915, val, I915_ERROR_CAPTURE,
"Manually set wedged engine mask = %llx", val);
return 0;
i915_gem_object_unpin_pages(obj);
}
-int __must_check i915_mutex_lock_interruptible(struct drm_device *dev);
+static inline int __must_check
+i915_mutex_lock_interruptible(struct drm_device *dev)
+{
+ return mutex_lock_interruptible(&dev->struct_mutex);
+}
+
int i915_gem_dumb_create(struct drm_file *file_priv,
struct drm_device *dev,
struct drm_mode_create_dumb *args);
struct i915_request *
i915_gem_find_active_request(struct intel_engine_cs *engine);
-static inline bool i915_reset_backoff(struct i915_gpu_error *error)
-{
- return unlikely(test_bit(I915_RESET_BACKOFF, &error->flags));
-}
-
static inline bool i915_terminally_wedged(struct i915_gpu_error *error)
{
return unlikely(test_bit(I915_WEDGED, &error->flags));
}
-static inline bool i915_reset_backoff_or_wedged(struct i915_gpu_error *error)
-{
- return i915_reset_backoff(error) | i915_terminally_wedged(error);
-}
-
static inline u32 i915_reset_count(struct i915_gpu_error *error)
{
return READ_ONCE(error->reset_count);
i915_reserve_fence(struct drm_i915_private *dev_priv);
void i915_unreserve_fence(struct drm_i915_fence_reg *fence);
-void i915_gem_revoke_fences(struct drm_i915_private *dev_priv);
void i915_gem_restore_fences(struct drm_i915_private *dev_priv);
void i915_gem_detect_bit_6_swizzle(struct drm_i915_private *dev_priv);
spin_unlock(&dev_priv->mm.object_stat_lock);
}
-static int
-i915_gem_wait_for_error(struct i915_gpu_error *error)
-{
- int ret;
-
- might_sleep();
-
- /*
- * Only wait 10 seconds for the gpu reset to complete to avoid hanging
- * userspace. If it takes that long something really bad is going on and
- * we should simply try to bail out and fail as gracefully as possible.
- */
- ret = wait_event_interruptible_timeout(error->reset_queue,
- !i915_reset_backoff(error),
- I915_RESET_TIMEOUT);
- if (ret == 0) {
- DRM_ERROR("Timed out waiting for the gpu reset to complete\n");
- return -EIO;
- } else if (ret < 0) {
- return ret;
- } else {
- return 0;
- }
-}
-
-int i915_mutex_lock_interruptible(struct drm_device *dev)
-{
- struct drm_i915_private *dev_priv = to_i915(dev);
- int ret;
-
- ret = i915_gem_wait_for_error(&dev_priv->gpu_error);
- if (ret)
- return ret;
-
- ret = mutex_lock_interruptible(&dev->struct_mutex);
- if (ret)
- return ret;
-
- return 0;
-}
-
static u32 __i915_gem_park(struct drm_i915_private *i915)
{
intel_wakeref_t wakeref;
intel_wakeref_t wakeref;
struct i915_vma *vma;
pgoff_t page_offset;
+ int srcu;
int ret;
/* Sanity check that we allow writing into this object */
goto err_unlock;
}
-
/* Now pin it into the GTT as needed */
vma = i915_gem_object_ggtt_pin(obj, NULL, 0, 0,
PIN_MAPPABLE |
if (ret)
goto err_unpin;
+ srcu = i915_reset_trylock(dev_priv);
+ if (srcu < 0) {
+ ret = srcu;
+ goto err_unpin;
+ }
+
ret = i915_vma_pin_fence(vma);
if (ret)
- goto err_unpin;
+ goto err_reset;
/* Finally, remap it using the new GTT offset */
ret = remap_io_mapping(area,
err_fence:
i915_vma_unpin_fence(vma);
+err_reset:
+ i915_reset_unlock(dev_priv, srcu);
err_unpin:
__i915_vma_unpin(vma);
err_unlock:
init_waitqueue_head(&dev_priv->gpu_error.wait_queue);
init_waitqueue_head(&dev_priv->gpu_error.reset_queue);
mutex_init(&dev_priv->gpu_error.wedge_mutex);
+ init_srcu_struct(&dev_priv->gpu_error.reset_backoff_srcu);
atomic_set(&dev_priv->mm.bsd_engine_dispatch_index, 0);
GEM_BUG_ON(atomic_read(&dev_priv->mm.free_count));
WARN_ON(dev_priv->mm.object_count);
+ cleanup_srcu_struct(&dev_priv->gpu_error.reset_backoff_srcu);
+
kmem_cache_destroy(dev_priv->priorities);
kmem_cache_destroy(dev_priv->dependencies);
kmem_cache_destroy(dev_priv->requests);
return 0;
}
+ ret = i915_reset_trylock(fence->i915);
+ if (ret < 0)
+ goto out_rpm;
+
fence_write(fence, vma);
fence->vma = vma;
list_move_tail(&fence->link, &fence->i915->mm.fence_list);
}
+ i915_reset_unlock(fence->i915, ret);
+ ret = 0;
+
+out_rpm:
intel_runtime_pm_put(fence->i915, wakeref);
- return 0;
+ return ret;
}
/**
}
/**
- * i915_gem_revoke_fences - revoke fence state
- * @dev_priv: i915 device private
- *
- * Removes all GTT mmappings via the fence registers. This forces any user
- * of the fence to reacquire that fence before continuing with their access.
- * One use is during GPU reset where the fence register is lost and we need to
- * revoke concurrent userspace access via GTT mmaps until the hardware has been
- * reset and the fence registers have been restored.
- */
-void i915_gem_revoke_fences(struct drm_i915_private *dev_priv)
-{
- int i;
-
- lockdep_assert_held(&dev_priv->drm.struct_mutex);
-
- for (i = 0; i < dev_priv->num_fence_regs; i++) {
- struct drm_i915_fence_reg *fence = &dev_priv->fence_regs[i];
-
- GEM_BUG_ON(fence->vma && fence->vma->fence != fence);
-
- if (fence->vma)
- i915_vma_revoke_mmap(fence->vma);
- }
-}
-
-/**
* i915_gem_restore_fences - restore fence state
* @dev_priv: i915 device private
*
atomic_t pending_fb_pin;
/**
- * State variable controlling the reset flow and count
- *
- * This is a counter which gets incremented when reset is triggered,
- *
- * Before the reset commences, the I915_RESET_BACKOFF bit is set
- * meaning that any waiters holding onto the struct_mutex should
- * relinquish the lock immediately in order for the reset to start.
- *
- * If reset is not completed successfully, the I915_WEDGE bit is
- * set meaning that hardware is terminally sour and there is no
- * recovery. All waiters on the reset_queue will be woken when
- * that happens.
- *
- * This counter is used by the wait_seqno code to notice that reset
- * event happened and it needs to restart the entire ioctl (since most
- * likely the seqno it waited for won't ever signal anytime soon).
- *
- * This is important for lock-free wait paths, where no contended lock
- * naturally enforces the correct ordering between the bail-out of the
- * waiter and the gpu reset work code.
- */
- unsigned long reset_count;
-
- /**
* flags: Control various stages of the GPU reset
*
- * #I915_RESET_BACKOFF - When we start a reset, we want to stop any
- * other users acquiring the struct_mutex. To do this we set the
- * #I915_RESET_BACKOFF bit in the error flags when we detect a reset
- * and then check for that bit before acquiring the struct_mutex (in
- * i915_mutex_lock_interruptible()?). I915_RESET_BACKOFF serves a
- * secondary role in preventing two concurrent global reset attempts.
+ * #I915_RESET_BACKOFF - When we start a global reset, we need to
+ * serialise with any other users attempting to do the same, and
+ * any global resources that may be clobber by the reset (such as
+ * FENCE registers).
*
* #I915_RESET_ENGINE[num_engines] - Since the driver doesn't need to
* acquire the struct_mutex to reset an engine, we need an explicit
#define I915_RESET_ENGINE 2
#define I915_WEDGED (BITS_PER_LONG - 1)
+ /** Number of times the device has been reset (global) */
+ u32 reset_count;
+
/** Number of times an engine has been reset */
u32 reset_engine_count[I915_NUM_ENGINES];
*/
wait_queue_head_t reset_queue;
+ struct srcu_struct reset_backoff_srcu;
+
struct i915_gpu_restart *restart;
};
engine->reset.prepare(engine);
}
+static void revoke_mmaps(struct drm_i915_private *i915)
+{
+ int i;
+
+ for (i = 0; i < i915->num_fence_regs; i++) {
+ struct drm_vma_offset_node *node;
+ struct i915_vma *vma;
+ u64 vma_offset;
+
+ vma = READ_ONCE(i915->fence_regs[i].vma);
+ if (!vma)
+ continue;
+
+ if (!i915_vma_has_userfault(vma))
+ continue;
+
+ GEM_BUG_ON(vma->fence != &i915->fence_regs[i]);
+ node = &vma->obj->base.vma_node;
+ vma_offset = vma->ggtt_view.partial.offset << PAGE_SHIFT;
+ unmap_mapping_range(i915->drm.anon_inode->i_mapping,
+ drm_vma_node_offset_addr(node) + vma_offset,
+ vma->size,
+ 1);
+ }
+}
+
static void reset_prepare(struct drm_i915_private *i915)
{
struct intel_engine_cs *engine;
reset_prepare_engine(engine);
intel_uc_sanitize(i915);
+ revoke_mmaps(i915);
}
static int gt_reset(struct drm_i915_private *i915, unsigned int stalled_mask)
return ret;
}
-struct __i915_reset {
- struct drm_i915_private *i915;
- unsigned int stalled_mask;
-};
-
-static int __i915_reset__BKL(void *data)
-{
- struct __i915_reset *arg = data;
- int err;
-
- err = intel_gpu_reset(arg->i915, ALL_ENGINES);
- if (err)
- return err;
-
- return gt_reset(arg->i915, arg->stalled_mask);
-}
-
-#if RESET_UNDER_STOP_MACHINE
-/*
- * XXX An alternative to using stop_machine would be to park only the
- * processes that have a GGTT mmap. By remote parking the threads (SIGSTOP)
- * we should be able to prevent their memmory accesses via the lost fence
- * registers over the course of the reset without the potential recursive
- * of mutexes between the pagefault handler and reset.
- *
- * See igt/gem_mmap_gtt/hang
- */
-#define __do_reset(fn, arg) stop_machine(fn, arg, NULL)
-#else
-#define __do_reset(fn, arg) fn(arg)
-#endif
-
static int do_reset(struct drm_i915_private *i915, unsigned int stalled_mask)
{
- struct __i915_reset arg = { i915, stalled_mask };
int err, i;
- err = __do_reset(__i915_reset__BKL, &arg);
+ /* Flush everyone currently using a resource about to be clobbered */
+ synchronize_srcu(&i915->gpu_error.reset_backoff_srcu);
+
+ err = intel_gpu_reset(i915, ALL_ENGINES);
for (i = 0; err && i < RESET_MAX_RETRIES; i++) {
- msleep(100);
- err = __do_reset(__i915_reset__BKL, &arg);
+ msleep(10 * (i + 1));
+ err = intel_gpu_reset(i915, ALL_ENGINES);
}
+ if (err)
+ return err;
- return err;
+ return gt_reset(i915, stalled_mask);
}
/**
* Reset the chip. Useful if a hang is detected. Marks the device as wedged
* on failure.
*
- * Caller must hold the struct_mutex.
- *
* Procedure is fairly simple:
* - reset the chip using the reset reg
* - re-init context state
wait_event(i915->gpu_error.reset_queue,
!test_bit(I915_RESET_BACKOFF,
&i915->gpu_error.flags));
- goto out;
+ goto out; /* piggy-back on the other reset */
}
+ /* Make sure i915_reset_trylock() sees the I915_RESET_BACKOFF */
+ synchronize_rcu_expedited();
+
/* Prevent any other reset-engine attempt. */
for_each_engine(engine, i915, tmp) {
while (test_and_set_bit(I915_RESET_ENGINE + engine->id,
intel_runtime_pm_put(i915, wakeref);
}
+int i915_reset_trylock(struct drm_i915_private *i915)
+{
+ struct i915_gpu_error *error = &i915->gpu_error;
+ int srcu;
+
+ rcu_read_lock();
+ while (test_bit(I915_RESET_BACKOFF, &error->flags)) {
+ rcu_read_unlock();
+
+ if (wait_event_interruptible(error->reset_queue,
+ !test_bit(I915_RESET_BACKOFF,
+ &error->flags)))
+ return -EINTR;
+
+ rcu_read_lock();
+ }
+ srcu = srcu_read_lock(&error->reset_backoff_srcu);
+ rcu_read_unlock();
+
+ return srcu;
+}
+
+void i915_reset_unlock(struct drm_i915_private *i915, int tag)
+__releases(&i915->gpu_error.reset_backoff_srcu)
+{
+ struct i915_gpu_error *error = &i915->gpu_error;
+
+ srcu_read_unlock(&error->reset_backoff_srcu, tag);
+}
+
bool i915_reset_flush(struct drm_i915_private *i915)
{
int err;
#include <linux/compiler.h>
#include <linux/types.h>
+#include <linux/srcu.h>
struct drm_i915_private;
struct intel_engine_cs;
void i915_reset_request(struct i915_request *rq, bool guilty);
bool i915_reset_flush(struct drm_i915_private *i915);
+int __must_check i915_reset_trylock(struct drm_i915_private *i915);
+void i915_reset_unlock(struct drm_i915_private *i915, int tag);
+
bool intel_has_gpu_reset(struct drm_i915_private *i915);
bool intel_has_reset_engine(struct drm_i915_private *i915);
struct intel_crtc_state *config;
- /* global reset count when the last flip was submitted */
- unsigned int reset_count;
-
/* Access to these should be protected by dev_priv->irq_lock. */
bool cpu_fifo_underrun_disabled;
bool pch_fifo_underrun_disabled;
/* Check that we can recover an unbind stuck on a hanging request */
- igt_global_reset_lock(i915);
-
mutex_lock(&i915->drm.struct_mutex);
err = hang_init(&h, i915);
if (err)
}
out_reset:
+ igt_global_reset_lock(i915);
fake_hangcheck(rq->i915, intel_engine_flag(rq->engine));
+ igt_global_reset_unlock(i915);
if (tsk) {
struct igt_wedge_me w;
hang_fini(&h);
unlock:
mutex_unlock(&i915->drm.struct_mutex);
- igt_global_reset_unlock(i915);
if (i915_terminally_wedged(&i915->gpu_error))
return -EIO;
init_waitqueue_head(&i915->gpu_error.wait_queue);
init_waitqueue_head(&i915->gpu_error.reset_queue);
+ init_srcu_struct(&i915->gpu_error.reset_backoff_srcu);
mutex_init(&i915->gpu_error.wedge_mutex);
i915->wq = alloc_ordered_workqueue("mock", 0);
projects / platform / kernel / linux-rpi.git / commitdiff