[Intel-gfx] [PATCH] drm/i915: Avoid calling i915_gem_object_unbind holding object lock
Chris Wilson
chris at chris-wilson.co.uk
Thu Dec 5 22:40:35 UTC 2019
In the extreme case, we may wish to wait on an rcu-barrier to reap stale
vm to purge the last of the object bindings. However, we are not allowed
to use rcu_barrier() beneath the dma_resv (i.e. object) lock and do not
take lightly the prospect of unlocking a mutex deep in the bowels of the
routine. i915_gem_object_unbind() itself does not need the object lock,
and it turns out the callers do not need to the unbind as part of a
locked sequence around set-cache-level, so rearrange the code to avoid
taking the object lock in the callers.
<4> [186.816311] ======================================================
<4> [186.816313] WARNING: possible circular locking dependency detected
<4> [186.816316] 5.4.0-rc8-CI-CI_DRM_7486+ #1 Tainted: G U
<4> [186.816318] ------------------------------------------------------
<4> [186.816320] perf_pmu/1321 is trying to acquire lock:
<4> [186.816322] ffff88849487c4d8 (&mm->mmap_sem#2){++++}, at: __might_fault+0x39/0x90
<4> [186.816331]
but task is already holding lock:
<4> [186.816333] ffffe8ffffa05008 (&cpuctx_mutex){+.+.}, at: perf_event_ctx_lock_nested+0xa9/0x1b0
<4> [186.816339]
which lock already depends on the new lock.
<4> [186.816341]
the existing dependency chain (in reverse order) is:
<4> [186.816343]
-> #6 (&cpuctx_mutex){+.+.}:
<4> [186.816349] __mutex_lock+0x9a/0x9d0
<4> [186.816352] perf_event_init_cpu+0xa4/0x140
<4> [186.816357] perf_event_init+0x19d/0x1cd
<4> [186.816362] start_kernel+0x372/0x4f4
<4> [186.816365] secondary_startup_64+0xa4/0xb0
<4> [186.816381]
-> #5 (pmus_lock){+.+.}:
<4> [186.816385] __mutex_lock+0x9a/0x9d0
<4> [186.816387] perf_event_init_cpu+0x6b/0x140
<4> [186.816404] cpuhp_invoke_callback+0x9b/0x9d0
<4> [186.816406] _cpu_up+0xa2/0x140
<4> [186.816409] do_cpu_up+0x61/0xa0
<4> [186.816411] smp_init+0x57/0x96
<4> [186.816413] kernel_init_freeable+0xac/0x1c7
<4> [186.816416] kernel_init+0x5/0x100
<4> [186.816419] ret_from_fork+0x24/0x50
<4> [186.816421]
-> #4 (cpu_hotplug_lock.rw_sem){++++}:
<4> [186.816424] cpus_read_lock+0x34/0xd0
<4> [186.816427] rcu_barrier+0xaa/0x190
<4> [186.816429] kernel_init+0x21/0x100
<4> [186.816431] ret_from_fork+0x24/0x50
<4> [186.816433]
-> #3 (rcu_state.barrier_mutex){+.+.}:
<4> [186.816436] __mutex_lock+0x9a/0x9d0
<4> [186.816438] rcu_barrier+0x23/0x190
<4> [186.816502] i915_gem_object_unbind+0x3a6/0x400 [i915]
<4> [186.816537] i915_gem_object_set_cache_level+0x32/0x90 [i915]
<4> [186.816571] i915_gem_object_pin_to_display_plane+0x5d/0x160 [i915]
<4> [186.816612] intel_pin_and_fence_fb_obj+0x9e/0x200 [i915]
<4> [186.816679] intel_plane_pin_fb+0x3f/0xd0 [i915]
<4> [186.816717] intel_prepare_plane_fb+0x130/0x520 [i915]
<4> [186.816722] drm_atomic_helper_prepare_planes+0x85/0x110
<4> [186.816761] intel_atomic_commit+0xc6/0x350 [i915]
<4> [186.816764] drm_atomic_helper_update_plane+0xed/0x110
<4> [186.816768] setplane_internal+0x97/0x190
<4> [186.816770] drm_mode_setplane+0xcd/0x190
<4> [186.816773] drm_ioctl_kernel+0xa7/0xf0
<4> [186.816775] drm_ioctl+0x2e1/0x390
<4> [186.816778] do_vfs_ioctl+0xa0/0x6f0
<4> [186.816780] ksys_ioctl+0x35/0x60
<4> [186.816782] __x64_sys_ioctl+0x11/0x20
<4> [186.816785] do_syscall_64+0x4f/0x210
<4> [186.816787] entry_SYSCALL_64_after_hwframe+0x49/0xbe
<4> [186.816789]
-> #2 (reservation_ww_class_mutex){+.+.}:
<4> [186.816793] __ww_mutex_lock.constprop.15+0xc3/0x1090
<4> [186.816795] ww_mutex_lock+0x39/0x70
<4> [186.816798] dma_resv_lockdep+0x10e/0x1f7
<4> [186.816800] do_one_initcall+0x58/0x2ff
<4> [186.816802] kernel_init_freeable+0x137/0x1c7
<4> [186.816804] kernel_init+0x5/0x100
<4> [186.816806] ret_from_fork+0x24/0x50
<4> [186.816808]
-> #1 (reservation_ww_class_acquire){+.+.}:
<4> [186.816811] dma_resv_lockdep+0xec/0x1f7
<4> [186.816813] do_one_initcall+0x58/0x2ff
<4> [186.816815] kernel_init_freeable+0x137/0x1c7
<4> [186.816817] kernel_init+0x5/0x100
<4> [186.816819] ret_from_fork+0x24/0x50
<4> [186.816820]
-> #0 (&mm->mmap_sem#2){++++}:
<4> [186.816824] __lock_acquire+0x1328/0x15d0
<4> [186.816826] lock_acquire+0xa7/0x1c0
<4> [186.816828] __might_fault+0x63/0x90
<4> [186.816831] _copy_to_user+0x1e/0x80
<4> [186.816834] perf_read+0x200/0x2b0
<4> [186.816836] vfs_read+0x96/0x160
<4> [186.816838] ksys_read+0x9f/0xe0
<4> [186.816839] do_syscall_64+0x4f/0x210
<4> [186.816841] entry_SYSCALL_64_after_hwframe+0x49/0xbe
<4> [186.816843]
other info that might help us debug this:
<4> [186.816846] Chain exists of:
&mm->mmap_sem#2 --> pmus_lock --> &cpuctx_mutex
<4> [186.816849] Possible unsafe locking scenario:
<4> [186.816851] CPU0 CPU1
<4> [186.816853] ---- ----
<4> [186.816854] lock(&cpuctx_mutex);
<4> [186.816856] lock(pmus_lock);
<4> [186.816858] lock(&cpuctx_mutex);
<4> [186.816860] lock(&mm->mmap_sem#2);
<4> [186.816861]
*** DEADLOCK ***
Closes: https://gitlab.freedesktop.org/drm/intel/issues/728
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
drivers/gpu/drm/i915/display/intel_display.c | 12 +++---
drivers/gpu/drm/i915/display/intel_overlay.c | 2 -
drivers/gpu/drm/i915/gem/i915_gem_domain.c | 41 ++++++--------------
3 files changed, 17 insertions(+), 38 deletions(-)
diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index eb0505a66ea8..cc57482436d4 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -2159,19 +2159,18 @@ intel_pin_and_fence_fb_obj(struct drm_framebuffer *fb,
* pin/unpin/fence and not more.
*/
wakeref = intel_runtime_pm_get(&dev_priv->runtime_pm);
- i915_gem_object_lock(obj);
atomic_inc(&dev_priv->gpu_error.pending_fb_pin);
- pinctl = 0;
-
- /* Valleyview is definitely limited to scanning out the first
+ /*
+ * Valleyview is definitely limited to scanning out the first
* 512MiB. Lets presume this behaviour was inherited from the
* g4x display engine and that all earlier gen are similarly
* limited. Testing suggests that it is a little more
* complicated than this. For example, Cherryview appears quite
* happy to scanout from anywhere within its global aperture.
*/
+ pinctl = 0;
if (HAS_GMCH(dev_priv))
pinctl |= PIN_MAPPABLE;
@@ -2183,7 +2182,8 @@ intel_pin_and_fence_fb_obj(struct drm_framebuffer *fb,
if (uses_fence && i915_vma_is_map_and_fenceable(vma)) {
int ret;
- /* Install a fence for tiled scan-out. Pre-i965 always needs a
+ /*
+ * Install a fence for tiled scan-out. Pre-i965 always needs a
* fence, whereas 965+ only requires a fence if using
* framebuffer compression. For simplicity, we always, when
* possible, install a fence as the cost is not that onerous.
@@ -2213,8 +2213,6 @@ intel_pin_and_fence_fb_obj(struct drm_framebuffer *fb,
i915_vma_get(vma);
err:
atomic_dec(&dev_priv->gpu_error.pending_fb_pin);
-
- i915_gem_object_unlock(obj);
intel_runtime_pm_put(&dev_priv->runtime_pm, wakeref);
return vma;
}
diff --git a/drivers/gpu/drm/i915/display/intel_overlay.c b/drivers/gpu/drm/i915/display/intel_overlay.c
index 8cfb785e761c..2a44b3be2600 100644
--- a/drivers/gpu/drm/i915/display/intel_overlay.c
+++ b/drivers/gpu/drm/i915/display/intel_overlay.c
@@ -758,10 +758,8 @@ static int intel_overlay_do_put_image(struct intel_overlay *overlay,
atomic_inc(&dev_priv->gpu_error.pending_fb_pin);
- i915_gem_object_lock(new_bo);
vma = i915_gem_object_pin_to_display_plane(new_bo,
0, NULL, PIN_MAPPABLE);
- i915_gem_object_unlock(new_bo);
if (IS_ERR(vma)) {
ret = PTR_ERR(vma);
goto out_pin_section;
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_domain.c b/drivers/gpu/drm/i915/gem/i915_gem_domain.c
index 808eb327a29b..f08082c19d91 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_domain.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_domain.c
@@ -187,19 +187,23 @@ int i915_gem_object_set_cache_level(struct drm_i915_gem_object *obj,
{
int ret;
- assert_object_held(obj);
-
if (obj->cache_level == cache_level)
return 0;
+ /* The cache-level will be applied when each vma is rebound. */
ret = i915_gem_object_unbind(obj, I915_GEM_OBJECT_UNBIND_ACTIVE);
if (ret)
return ret;
- /* The cache-level will be applied when each vma is rebound. */
-
- i915_gem_object_set_cache_coherency(obj, cache_level);
- obj->cache_dirty = true; /* Always invalidate stale cachelines */
+ ret = i915_gem_object_lock_interruptible(obj);
+ if (ret == 0) {
+ if (obj->cache_level != cache_level) {
+ /* Always invalidate stale cachelines */
+ i915_gem_object_set_cache_coherency(obj, cache_level);
+ obj->cache_dirty = true;
+ }
+ i915_gem_object_unlock(obj);
+ }
return 0;
}
@@ -282,20 +286,7 @@ int i915_gem_set_caching_ioctl(struct drm_device *dev, void *data,
goto out;
}
- if (obj->cache_level == level)
- goto out;
-
- ret = i915_gem_object_wait(obj,
- I915_WAIT_INTERRUPTIBLE,
- MAX_SCHEDULE_TIMEOUT);
- if (ret)
- goto out;
-
- ret = i915_gem_object_lock_interruptible(obj);
- if (ret == 0) {
- ret = i915_gem_object_set_cache_level(obj, level);
- i915_gem_object_unlock(obj);
- }
+ ret = i915_gem_object_set_cache_level(obj, level);
out:
i915_gem_object_put(obj);
@@ -318,8 +309,6 @@ i915_gem_object_pin_to_display_plane(struct drm_i915_gem_object *obj,
struct i915_vma *vma;
int ret;
- assert_object_held(obj);
-
/* Frame buffer must be in LMEM (no migration yet) */
if (HAS_LMEM(i915) && !i915_gem_object_is_lmem(obj))
return ERR_PTR(-EINVAL);
@@ -362,13 +351,7 @@ i915_gem_object_pin_to_display_plane(struct drm_i915_gem_object *obj,
vma->display_alignment = max_t(u64, vma->display_alignment, alignment);
- __i915_gem_object_flush_for_display(obj);
-
- /*
- * It should now be out of any other write domains, and we can update
- * the domain values for our changes.
- */
- obj->read_domains |= I915_GEM_DOMAIN_GTT;
+ i915_gem_object_flush_if_display(obj);
return vma;
}
--
2.24.0
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