drm/amd/display: Add comment explaining context free

This comment explains a previous change that adds some complexity
to the context free in dc:

commit 9ad58779a895 ("drm/amd/display: Fix accessing freed memory")

Signed-off-by: Corbin McElhanney <corbin.mcelhanney@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

diff --git a/drivers/gpu/drm/amd/display/dc/core/dc.c b/drivers/gpu/drm/amd/display/dc/core/dc.c
index 477024c467e63292e07c4effdcf42a3a596f34a9..33c3d88b1c86632c339295132eb77a539ebf63b6 100644 (file)
--- a/drivers/gpu/drm/amd/display/dc/core/dc.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc.c
@@ -1740,6 +1740,15 @@ void dc_update_planes_and_stream(struct dc *dc,
        }
 
        if (core_dc->current_context != context) {
+
+               /* Since memory free requires elevated IRQL, an interrupt
+                * request is generated by mem free. If this happens
+                * between freeing and reassigning the context, our vsync
+                * interrupt will call into dc and cause a memory
+                * corruption BSOD. Hence, we first reassign the context,
+                * then free the old context.
+                */
+
                struct validate_context *old = core_dc->current_context;
 
                core_dc->current_context = context;