linux-kernel - [Patch] UML: spurious interrupt freezes guest

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Date:	Mon, 19 Jan 2009 20:53:25 -0700
From:	Shane Hathaway <shane@...hawaymix.org>
To:	linux-kernel@...r.kernel.org,
	user-mode-linux-devel@...ts.sourceforge.net
Subject: [Patch] UML: spurious interrupt freezes guest

A new instance of user mode linux that I created over the past couple of
days worked pretty well except that it had a habit of freezing after a
few minutes.  Every time it froze, the last message on the console was
either:

spurious interrupt in ubd_handler, err = 4

or:

spurious interrupt in ubd_handler, err = 0

This message is generated by arch/um/drivers/ubd_kern.c.  I did not work
out the cause of the spurious interrupts, but I did come up with a patch
that makes the guest recover from spurious interrupts without freezing.
 It appears that the interrupt handler needs to be reactivated before
every exit of ubd_handler().  The patch is below.

Shane

--- linux-2.6.27.12-orig/arch/um/drivers/ubd_kern.c
+++ linux-2.6.27.12/arch/um/drivers/ubd_kern.c
@@ -489,6 +489,7 @@
                                break;
                        printk(KERN_ERR "spurious interrupt in
ubd_handler, "
                               "err = %d\n", -n);
+                       reactivate_fd(thread_fd, UBD_IRQ);
                        return;
                }

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