Answer Posted / sriniv

Take three tasks A,B and C.

A - High.
B - Medium.
C - Low.

C is scheduled and running and locks a resource which is
shared with A. Now B is scheduled and taked the CPU time so
it starts running keeping C in wait state.

Now A is scheduled which is the higher priority task than B
and C and gets the CPU time and it starts running. But it
needs the shared resource which is locked by task C. So A
waits for that resource.

Now CPU starts servicing task B as it has higher priority
than C. A is suppose to wait till task B is finished even
though it has highest priority than B. To avoid this
situation exchange the priority levels of A and C. After
this C will become highest priority and gets the CPU time
by suspending task B. Task C will be serviced and releases
resource shared with task A. As soon as task C is released
the shared resource change the prority levels of A and C
again. Now A will become highest priority than C and CPU
starts running Task A.

This is called Proirity inversion.

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