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Index: head/sys/x86/x86/mp_x86.c
===================================================================
--- head/sys/x86/x86/mp_x86.c
+++ head/sys/x86/x86/mp_x86.c
@@ -1425,16 +1425,36 @@
#else
npxsuspend(susppcbs[cpu]->sp_fpususpend);
#endif
- wbinvd();
- CPU_SET_ATOMIC(cpu, &suspended_cpus);
/*
- * Hack for xen, which does not use resumectx() so never
- * uses the next clause: set resuming_cpus early so that
- * resume_cpus() can wait on the same bitmap for acpi and
- * xen. resuming_cpus now means eventually_resumable_cpus.
+ * suspended_cpus is cleared shortly after each AP is restarted
+ * by a Startup IPI, so that the BSP can proceed to restarting
+ * the next AP.
+ *
+ * resuming_cpus gets cleared when the AP completes
+ * initialization after having been released by the BSP.
+ * resuming_cpus is probably not the best name for the
+ * variable, because it is actually a set of processors that
+ * haven't resumed yet and haven't necessarily started resuming.
+ *
+ * Note that suspended_cpus is meaningful only for ACPI suspend
+ * as it's not really used for Xen suspend since the APs are
+ * automatically restored to the running state and the correct
+ * context. For the same reason resumectx is never called in
+ * that case.
*/
+ CPU_SET_ATOMIC(cpu, &suspended_cpus);
CPU_SET_ATOMIC(cpu, &resuming_cpus);
+
+ /*
+ * Invalidate the cache after setting the global status bits.
+ * The last AP to set its bit may end up being an Owner of the
+ * corresponding cache line in MOESI protocol. The AP may be
+ * stopped before the cache line is written to the main memory.
+ */
+ wbinvd();
} else {
+ /* Indicate that we have restarted and restored the context. */
+ CPU_CLR_ATOMIC(cpu, &suspended_cpus);
#ifdef __amd64__
fpuresume(susppcbs[cpu]->sp_fpususpend);
#else
@@ -1444,9 +1464,6 @@
initializecpu();
PCPU_SET(switchtime, 0);
PCPU_SET(switchticks, ticks);
-
- /* Indicate that we are resuming */
- CPU_CLR_ATOMIC(cpu, &suspended_cpus);
}
/* Wait for resume directive */

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