VirtIO-GPU commands may be processed outside of main-loop, from a CPU
thread. This results in GL context switch failure because context is held
by main-loop thread when GL is invoked from CPU thread. Always release GL
context after performing GL operations such that other threads could take
over the context.

 0  SDL_GL_MakeCurrent() (libSDL3)
 1  SDL_GL_MakeCurrent_REAL() (libSDL2)
 2  sdl2_gl_make_context_current() (ui/sdl2-gl.c:201)
 3  make_current() (virglrenderer.c:639)
 4  vrend_finish_context_switch() (vrend_renderer.c:11630)
 5  vrend_hw_switch_context() (vrend_renderer.c:11613)
 6  vrend_renderer_force_ctx_0() (vrend_renderer.c:12986)
 7  virgl_renderer_force_ctx_0() (virglrenderer.c:460)
 8  virtio_gpu_virgl_process_cmd() (virtio-gpu-virgl.c:1013)
 9  virtio_gpu_process_cmdq() (virtio-gpu.c:1050)
 10 virtio_gpu_gl_handle_ctrl() (virtio-gpu-gl.c:86)
 11 aio_bh_poll() (util/async.c)
 12 aio_poll() (util/aio-posix.c)
 13 blk_pwrite() (block/block-gen.c:1985)
 14 pflash_update() (pflash_cfi01.c:396)
 15 pflash_write() (pflash_cfi01.c:541)
 16 memory_region_dispatch_write() (system/memory.c:1554)
 17 flatview_write() (system/physmem.c:3333)
 18 address_space_write() (system/physmem.c:3453)
 19 kvm_cpu_exec() (accel/kvm/kall-all.c:3248)
 20 kvm_vcpu_thread_fn() (accel/kvm/kaccel-ops.c:53)

Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---
 ui/sdl2-gl.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/ui/sdl2-gl.c b/ui/sdl2-gl.c
index 55e22a7a3d59..936b15f737d8 100644
--- a/ui/sdl2-gl.c
+++ b/ui/sdl2-gl.c
@@ -57,6 +57,8 @@ static void sdl2_gl_render_surface(struct sdl2_console *scon)
 
     surface_gl_render_texture(scon->gls, scon->surface);
     SDL_GL_SwapWindow(scon->real_window);
+
+    SDL_GL_MakeCurrent(scon->real_window, NULL);
 }
 
 void sdl2_gl_update(DisplayChangeListener *dcl,
@@ -73,6 +75,8 @@ void sdl2_gl_update(DisplayChangeListener *dcl,
     SDL_GL_MakeCurrent(scon->real_window, scon->winctx);
     surface_gl_update_texture(scon->gls, scon->surface, x, y, w, h);
     scon->updates++;
+
+    SDL_GL_MakeCurrent(scon->real_window, NULL);
 }
 
 void sdl2_gl_switch(DisplayChangeListener *dcl,
@@ -91,6 +95,7 @@ void sdl2_gl_switch(DisplayChangeListener *dcl,
     if (surface_is_placeholder(new_surface) && qemu_console_get_index(dcl->con)) {
         qemu_gl_fini_shader(scon->gls);
         scon->gls = NULL;
+        SDL_GL_MakeCurrent(scon->real_window, NULL);
         sdl2_window_destroy(scon);
         return;
     }
@@ -105,6 +110,8 @@ void sdl2_gl_switch(DisplayChangeListener *dcl,
     }
 
     surface_gl_create_texture(scon->gls, scon->surface);
+
+    SDL_GL_MakeCurrent(scon->real_window, NULL);
 }
 
 void sdl2_gl_refresh(DisplayChangeListener *dcl)
-- 
2.52.0