libdrm atomic_add_unless() may reverse meaning of return value
David Shao
davshao at gmail.com
Mon Mar 6 00:49:57 PST 2017
For those who have frustrating glitches with applications
such as glxgears on Intel integrated graphics, the
following libdrm bug report may be of interest.
https://bugs.freedesktop.org/show_bug.cgi?id=100077
"libdrm atomic_add_unless() may reverse return value meaning"
A one character patch allows glxgears to run on
DragonFly using a hacked version of pkgsrc on an
Intel IvyBridge integrated graphics machine.
--- xf86atomic.h.orig 2015-09-22 04:34:51.000000000 +0000
+++ xf86atomic.h
@@ -111,7 +111,7 @@ static inline int atomic_add_unless(atom
c = atomic_read(v);
while (c != unless && (old = atomic_cmpxchg(v, c, c + add)) != c)
c = old;
- return c == unless;
+ return c != unless;
}
#endif
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