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. Testcase: igt/gem_mmap_gtt/hang Fixes: eb8d0f5af4ec ("drm/i915: Remove GPU reset dependence on struct_mutex") Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxx> --- drivers/gpu/drm/i915/i915_debugfs.c | 12 +- drivers/gpu/drm/i915/i915_drv.h | 18 +-- drivers/gpu/drm/i915/i915_gem.c | 56 +++------- drivers/gpu/drm/i915/i915_gem_fence_reg.c | 31 +----- drivers/gpu/drm/i915/i915_gpu_error.h | 12 +- drivers/gpu/drm/i915/i915_reset.c | 103 +++++++++++------- drivers/gpu/drm/i915/i915_reset.h | 4 + .../gpu/drm/i915/selftests/mock_gem_device.c | 1 + 8 files changed, 103 insertions(+), 134 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c index fa2c226fc779..2cea263b4d79 100644 --- a/drivers/gpu/drm/i915/i915_debugfs.c +++ b/drivers/gpu/drm/i915/i915_debugfs.c @@ -1281,14 +1281,11 @@ static int i915_hangcheck_info(struct seq_file *m, void *unused) 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"); @@ -3885,9 +3882,6 @@ i915_wedged_set(void *data, u64 val) * 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; diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h index 22da9df1f0a7..f7a0e5185874 100644 --- a/drivers/gpu/drm/i915/i915_drv.h +++ b/drivers/gpu/drm/i915/i915_drv.h @@ -2987,7 +2987,12 @@ i915_gem_obj_finish_shmem_access(struct drm_i915_gem_object *obj) 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); @@ -3004,21 +3009,11 @@ int __must_check i915_gem_set_global_seqno(struct drm_device *dev, u32 seqno); 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); @@ -3091,7 +3086,6 @@ struct drm_i915_fence_reg * 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); diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index e802af64d628..caccff87a2a1 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -100,47 +100,6 @@ static void i915_gem_info_remove_obj(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; @@ -1869,6 +1828,7 @@ vm_fault_t i915_gem_fault(struct vm_fault *vmf) 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 */ @@ -1908,7 +1868,6 @@ vm_fault_t i915_gem_fault(struct vm_fault *vmf) goto err_unlock; } - /* Now pin it into the GTT as needed */ vma = i915_gem_object_ggtt_pin(obj, NULL, 0, 0, PIN_MAPPABLE | @@ -1946,9 +1905,15 @@ vm_fault_t i915_gem_fault(struct vm_fault *vmf) if (ret) goto err_unpin; + srcu = i915_reset_lock(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, @@ -1969,6 +1934,8 @@ vm_fault_t i915_gem_fault(struct vm_fault *vmf) err_fence: i915_vma_unpin_fence(vma); +err_reset: + i915_reset_unlock(dev_priv, srcu); err_unpin: __i915_vma_unpin(vma); err_unlock: @@ -5324,6 +5291,7 @@ int i915_gem_init_early(struct drm_i915_private *dev_priv) 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.srcu); atomic_set(&dev_priv->mm.bsd_engine_dispatch_index, 0); @@ -5356,6 +5324,8 @@ void i915_gem_cleanup_early(struct drm_i915_private *dev_priv) GEM_BUG_ON(atomic_read(&dev_priv->mm.free_count)); WARN_ON(dev_priv->mm.object_count); + cleanup_srcu_struct(&dev_priv->gpu_error.srcu); + kmem_cache_destroy(dev_priv->priorities); kmem_cache_destroy(dev_priv->dependencies); kmem_cache_destroy(dev_priv->requests); diff --git a/drivers/gpu/drm/i915/i915_gem_fence_reg.c b/drivers/gpu/drm/i915/i915_gem_fence_reg.c index 46e259661294..069db4175971 100644 --- a/drivers/gpu/drm/i915/i915_gem_fence_reg.c +++ b/drivers/gpu/drm/i915/i915_gem_fence_reg.c @@ -240,6 +240,10 @@ static int fence_update(struct drm_i915_fence_reg *fence, i915_vma_flush_writes(old); } + ret = i915_reset_lock(fence->i915); + if (ret < 0) + return ret; + if (fence->vma && fence->vma != vma) { /* Ensure that all userspace CPU access is completed before * stealing the fence. @@ -272,6 +276,7 @@ static int fence_update(struct drm_i915_fence_reg *fence, list_move_tail(&fence->link, &fence->i915->mm.fence_list); } + i915_reset_unlock(fence->i915, ret); return 0; } @@ -435,32 +440,6 @@ void i915_unreserve_fence(struct drm_i915_fence_reg *fence) list_add(&fence->link, &fence->i915->mm.fence_list); } -/** - * 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 diff --git a/drivers/gpu/drm/i915/i915_gpu_error.h b/drivers/gpu/drm/i915/i915_gpu_error.h index 53b1f22dd365..4e797c552b96 100644 --- a/drivers/gpu/drm/i915/i915_gpu_error.h +++ b/drivers/gpu/drm/i915/i915_gpu_error.h @@ -231,12 +231,10 @@ struct i915_gpu_error { /** * 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 @@ -272,6 +270,8 @@ struct i915_gpu_error { */ wait_queue_head_t reset_queue; + struct srcu_struct srcu; + struct i915_gpu_restart *restart; }; diff --git a/drivers/gpu/drm/i915/i915_reset.c b/drivers/gpu/drm/i915/i915_reset.c index 4462007a681c..0a6784cec4fd 100644 --- a/drivers/gpu/drm/i915/i915_reset.c +++ b/drivers/gpu/drm/i915/i915_reset.c @@ -639,6 +639,31 @@ static void reset_prepare_engine(struct intel_engine_cs *engine) 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 i915_vma *vma = i915->fence_regs[i].vma; + struct drm_vma_offset_node *node; + u64 vma_offset; + + if (!vma) + continue; + + GEM_BUG_ON(vma->fence != &i915->fence_regs[i]); + if (!i915_vma_has_userfault(vma)) + continue; + + 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; @@ -648,6 +673,7 @@ static void reset_prepare(struct drm_i915_private *i915) reset_prepare_engine(engine); intel_uc_sanitize(i915); + revoke_mmaps(i915); } static int gt_reset(struct drm_i915_private *i915, unsigned int stalled_mask) @@ -911,50 +937,22 @@ bool i915_gem_unset_wedged(struct drm_i915_private *i915) 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.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); } /** @@ -1274,9 +1272,12 @@ void i915_handle_error(struct drm_i915_private *i915, 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_lock() 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, @@ -1300,6 +1301,32 @@ void i915_handle_error(struct drm_i915_private *i915, intel_runtime_pm_put(i915, wakeref); } +int i915_reset_lock(struct drm_i915_private *i915) +{ + int srcu; + + rcu_read_lock(); + while (test_bit(I915_RESET_BACKOFF, &i915->gpu_error.flags)) { + rcu_read_unlock(); + + if (wait_event_interruptible(i915->gpu_error.reset_queue, + !test_bit(I915_RESET_BACKOFF, + &i915->gpu_error.flags))) + return -EINTR; + + rcu_read_lock(); + } + srcu = srcu_read_lock(&i915->gpu_error.srcu); + rcu_read_unlock(); + + return srcu; +} + +void i915_reset_unlock(struct drm_i915_private *i915, int tag) +{ + srcu_read_unlock(&i915->gpu_error.srcu, tag); +} + bool i915_reset_flush(struct drm_i915_private *i915) { int err; diff --git a/drivers/gpu/drm/i915/i915_reset.h b/drivers/gpu/drm/i915/i915_reset.h index f2d347f319df..eb412e0158da 100644 --- a/drivers/gpu/drm/i915/i915_reset.h +++ b/drivers/gpu/drm/i915/i915_reset.h @@ -9,6 +9,7 @@ #include <linux/compiler.h> #include <linux/types.h> +#include <linux/srcu.h> struct drm_i915_private; struct intel_engine_cs; @@ -32,6 +33,9 @@ int i915_reset_engine(struct intel_engine_cs *engine, void i915_reset_request(struct i915_request *rq, bool guilty); bool i915_reset_flush(struct drm_i915_private *i915); +int i915_reset_lock(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); diff --git a/drivers/gpu/drm/i915/selftests/mock_gem_device.c b/drivers/gpu/drm/i915/selftests/mock_gem_device.c index 14ae46fda49f..074a0d9cbf26 100644 --- a/drivers/gpu/drm/i915/selftests/mock_gem_device.c +++ b/drivers/gpu/drm/i915/selftests/mock_gem_device.c @@ -189,6 +189,7 @@ struct drm_i915_private *mock_gem_device(void) init_waitqueue_head(&i915->gpu_error.wait_queue); init_waitqueue_head(&i915->gpu_error.reset_queue); + init_srcu_struct(&i915->gpu_error.srcu); mutex_init(&i915->gpu_error.wedge_mutex); i915->wq = alloc_ordered_workqueue("mock", 0); -- 2.20.1 _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
