I realized that the piece of code at the end of the old NMI handler was
still necessary. I have attached a patch to the previous version to fix
the problem. The full version of the patch with this fix is on my web
page at http://home.attbi.com/~minyard/linux-nmi-v8.diff.
-Corey
--- linux.v8/arch/i386/kernel/nmi.c Thu Oct 24 20:53:04 2002
+++ linux/arch/i386/kernel/nmi.c Fri Oct 25 08:21:22 2002
@@ -208,30 +208,29 @@
if (!handled)
unknown_nmi_error(regs, cpu);
-#if 0
- /*
- * It MAY be possible to only call handlers until one returns
- * that it handled the NMI, if, we do the following. Assuming
- * that all the incoming signals causing NMIs are
- * level-triggered, this code will cause another NMI
- * immediately if the incoming signal is still asserted. I
- * don't know if the assumption is correct or if it's better
- * to call all the handlers or do the I/O.
- *
- * I'm pretty sure that this won't work with the performance
- * registers NMI output, so I'm guessing that this won't work.
- */
else {
/*
* Reassert NMI in case it became active meanwhile
- * as it's edge-triggered.
+ * as it's edge-triggered. Don't do this if the NMI
+ * wasn't handled to avoid an infinite NMI loop.
+ *
+ * This is necessary in case we have another external
+ * NMI while processing this one. The external NMIs
+ * are level-generated, into the processor NMIs are
+ * edge-triggered, so if you have one NMI source
+ * come in while another is already there, the level
+ * will never go down to cause another edge, and
+ * no more NMIs will happen. This does NOT apply
+ * to internally generated NMIs, though, so you
+ * can't use the same trick to only call one handler
+ * at a time. Otherwise, if two internal NMIs came
+ * in at the same time you might miss one.
*/
outb(0x8f, 0x70);
inb(0x71); /* dummy */
outb(0x0f, 0x70);
inb(0x71); /* dummy */
}
-#endif
}
void __init init_nmi(void)
-
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