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drm/i915/dsb: remove atomic operations

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The current dsb API is not really prepared to handle multithread access.
I was debugging an issue that ended up fixed by commit a096883dda
("drm/i915/dsb: Remove PIN_MAPPABLE from the DSB object VMA") and was
puzzled how these atomic operations were guaranteeing atomicity.

	if (atomic_add_return(1, &dsb->refcount) != 1)
		return dsb;

Thread A could still be initializing dsb struct (and even fail in the
middle) while thread B would take a reference and use it (even
derefencing a NULL cmd_buf).

I don't think the atomic operations here will help much if this were
to support multithreaded scenario in future, so just remove them to
avoid confusion.

v2: Use refcount++ != 0 instead of ++refcount != 1 (from Ville)

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191111205024.22853-2-lucas.demarchi@intel.com
Link: https://patchwork.freedesktop.org/patch/msgid/20191116011539.18230-1-lucas.demarchi@intel.com
This commit is contained in:
Lucas De Marchi
2019-11-15 17:15:39 -08:00
parent c50bb4dd1f
commit ac4eead379
2 changed files with 6 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
drivers/gpu/drm/i915/display/intel_dsb.c
View File

@@ -107,7 +107,7 @@ intel_dsb_get(struct intel_crtc *crtc)
if (!HAS_DSB(i915)) if (!HAS_DSB(i915))
return dsb; return dsb;
if (atomic_add_return(1, &dsb->refcount) != 1) if (dsb->refcount++ != 0)
return dsb; return dsb;
dsb->id = DSB1; dsb->id = DSB1;
@@ -123,7 +123,7 @@ intel_dsb_get(struct intel_crtc *crtc)
if (IS_ERR(vma)) { if (IS_ERR(vma)) {
DRM_ERROR("Vma creation failed\n"); DRM_ERROR("Vma creation failed\n");
i915_gem_object_put(obj); i915_gem_object_put(obj);
atomic_dec(&dsb->refcount); dsb->refcount--;
goto err; goto err;
} }
@@ -132,7 +132,7 @@ intel_dsb_get(struct intel_crtc *crtc)
DRM_ERROR("Command buffer creation failed\n"); DRM_ERROR("Command buffer creation failed\n");
i915_vma_unpin_and_release(&vma, 0); i915_vma_unpin_and_release(&vma, 0);
dsb->cmd_buf = NULL; dsb->cmd_buf = NULL;
atomic_dec(&dsb->refcount); dsb->refcount--;
goto err; goto err;
} }
dsb->vma = vma; dsb->vma = vma;
@@ -158,10 +158,10 @@ void intel_dsb_put(struct intel_dsb *dsb)
if (!HAS_DSB(i915)) if (!HAS_DSB(i915))
return; return;
if (WARN_ON(atomic_read(&dsb->refcount) == 0)) if (WARN_ON(dsb->refcount == 0))
return; return;
if (atomic_dec_and_test(&dsb->refcount)) { if (--dsb->refcount == 0) {
i915_vma_unpin_and_release(&dsb->vma, I915_VMA_RELEASE_MAP); i915_vma_unpin_and_release(&dsb->vma, I915_VMA_RELEASE_MAP);
dsb->cmd_buf = NULL; dsb->cmd_buf = NULL;
dsb->free_pos = 0; dsb->free_pos = 0;

2
drivers/gpu/drm/i915/display/intel_dsb.h
View File

@@ -22,7 +22,7 @@ enum dsb_id {
}; };
struct intel_dsb { struct intel_dsb {
atomic_t refcount; long refcount;
enum dsb_id id; enum dsb_id id;
u32 *cmd_buf; u32 *cmd_buf;
struct i915_vma *vma; struct i915_vma *vma;