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xen: save previous spinlock when blocking

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A spinlock can be interrupted while spinning, so make sure we preserve
the previous lock of interest if we're taking a lock from within an
interrupt handler.

We also need to deal with the case where the blocking path gets
interrupted between testing to see if the lock is free and actually
blocking.  If we get interrupted there and end up in the state where
the lock is free but the irq isn't pending, then we'll block
indefinitely in the hypervisor.  This fix is to make sure that any
nested lock-takers will always leave the irq pending if there's any
chance the outer lock became free.

Signed-off-by: Jeremy Fitzhardinge <[email protected]>
Acked-by: Jan Beulich <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Jeremy Fitzhardinge 2008-08-20 17:02:18 -07:00 • committed by Ingo Molnar
commit 168d2f464a
3 changed files with 77 additions and 15 deletions
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2
include/xen/events.h
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@ -46,6 +46,8 @@ extern void xen_irq_resume(void);
/* Clear an irq's pending state, in preparation for polling on it */
void xen_clear_irq_pending(int irq);
void xen_set_irq_pending(int irq);
bool xen_test_irq_pending(int irq);
/* Poll waiting for an irq to become pending. In the usual case, the
irq will be disabled so it won't deliver an interrupt. */