d4bd39f1a5
It's possible for present_execute_copy to enqueue a vblank even when TearFree is used, specifically when the present_queue_vblank in present_scmd_pixmap fails and the subsequent vblank enqueue in present_execute_copy somehow doesn't. This could happen if the DRM event queue is exhausted when present_queue_vblank is called, but is no longer exhausted by the time present_execute_copy is reached. This exceedingly unlikely chain of events can lead to a vblank getting enqueued a second time by the TearFree machinery in present_execute, which is not good. Although this scenario is very unlikely, prevent it by first checking that the vblank wasn't enqueued by present_execute_copy before attempting to enqueue it for TearFree. Signed-off-by: Sultan Alsawaf <sultan@kerneltoast.com> Acked-by: Martin Roukala <martin.roukala@mupuf.org>
X Server
The X server accepts requests from client applications to create windows, which are (normally rectangular) "virtual screens" that the client program can draw into.
Windows are then composed on the actual screen by the X server (or by a separate composite manager) as directed by the window manager, which usually communicates with the user via graphical controls such as buttons and draggable titlebars and borders.
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