Here's a backtrace of Xwayland after triggering this bug:
#0 0x00007f9d27227017 in __GI___writev (fd=15, iov=iov@entry=0x7ffc7e53bec0,
iovcnt=iovcnt@entry=0) at ../sysdeps/unix/sysv/linux/writev.c:26
#1 0x000055912d2bb56e in _XSERVTransSocketWritev (ciptr=0x55912fa10090,
buf=0x7ffc7e53bec0, size=<optimized out>) at
/usr/include/X11/Xtrans/Xtranssock.c:2367
#2 0x000055912d2b5fcd in FlushClient (who=who@entry=0x55912f9536b0,
oc=oc@entry=0x55912f922c30, __extraBuf=__extraBuf@entry=0x7ffc7e53c010,
extraCount=extraCount@entry=-4) at ../../../../os/io.c:882
#3 0x000055912d2b659e in WriteToClient (who=who@entry=0x55912f9536b0,
count=count@entry=-4, __buf=__buf@entry=0x7ffc7e53c010) at
../../../../os/io.c:795
#4 0x000055912d21cdac in proc_dri3_buffers_from_pixmap (client=0x55912f9536b0)
at ../../../../dri3/dri3_request.c:555
#5 0x000055912d280dc8 in Dispatch () at ../../../../dix/dispatch.c:478
#6 0x000055912d284dc8 in dix_main (argc=12, argv=0x7ffc7e53c218,
envp=<optimized out>) at ../../../../dix/main.c:276
#7 0x00007f9d2715aa87 in __libc_start_main (main=0x55912d158520 <main>,
argc=12, argv=0x7ffc7e53c218, init=<optimized out>, fini=<optimized out>,
rtld_fini=<optimized out>, stack_end=0x7ffc7e53c208) at ../csu/libc-start.c:310
#8 0x000055912d15855a in _start ()
