drm/i915/dsb: remove atomic operations (ac4eead3) · Commits · 戴 / test

The current dsb API is not really prepared to handle multithread access. I was debugging an issue that ended up fixed by commit ("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

drivers/gpu/drm/i915/display/intel_dsb.c

+5 −5

Original line number	Diff line number	Diff line
		@@ -107,7 +107,7 @@ intel_dsb_get(struct intel_crtc *crtc)
		if (!HAS_DSB(i915))
		return dsb;

		if (atomic_add_return(1, &dsb->refcount) != 1)
		if (dsb->refcount++ != 0)
		return dsb;

		dsb->id = DSB1;
		@@ -123,7 +123,7 @@ intel_dsb_get(struct intel_crtc *crtc)
		if (IS_ERR(vma)) {
		DRM_ERROR("Vma creation failed\n");
		i915_gem_object_put(obj);
		atomic_dec(&dsb->refcount);
		dsb->refcount--;
		goto err;
		}

		@@ -132,7 +132,7 @@ intel_dsb_get(struct intel_crtc *crtc)
		DRM_ERROR("Command buffer creation failed\n");
		i915_vma_unpin_and_release(&vma, 0);
		dsb->cmd_buf = NULL;
		atomic_dec(&dsb->refcount);
		dsb->refcount--;
		goto err;
		}
		dsb->vma = vma;
		@@ -158,10 +158,10 @@ void intel_dsb_put(struct intel_dsb *dsb)
		if (!HAS_DSB(i915))
		return;

		if (WARN_ON(atomic_read(&dsb->refcount) == 0))
		if (WARN_ON(dsb->refcount == 0))
		return;

		if (atomic_dec_and_test(&dsb->refcount)) {
		if (--dsb->refcount == 0) {
		i915_vma_unpin_and_release(&dsb->vma, I915_VMA_RELEASE_MAP);
		dsb->cmd_buf = NULL;
		dsb->free_pos = 0;

drivers/gpu/drm/i915/display/intel_dsb.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -22,7 +22,7 @@ enum dsb_id {
		};

		struct intel_dsb {
		atomic_t refcount;
		long refcount;
		enum dsb_id id;
		u32 *cmd_buf;
		struct i915_vma *vma;

Admin message