Xen devel - Apr 2006 - [PATCH 4/5] pciback: deferred handling of pci configuration space accesses

Some of the linux PCI functions called by the virtual configuration
space handlers (both the ones added by this patch and the ones currently
in the xen-unstable tree) were making calls into ACPI code which uses
semaphores. Since semaphores can not be locked while atomic (because
they can sleep), I changed the way the PCI backend responds to requests
from the frontend. Previously, the virtual configuration space handlers
ran in the same context as the event channel interrupt handler (which
was often atomic if not always atomic). Now the interrupt handlers
schedules a callback function (a bottom half) in the system work queue
(keventd) that will get called in process context at a slightly later
time. This allows the handlers in the virtual configuration space to
call any core PCI function regardless of whether it will sleep or not.

Signed-off-by: Ryan Wilson <hap9@epoch.ncsc.mil>


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