debugobjects: Prevent RT lock assertion due to pi_blocked_on in fill_pool

Executive Summary

This vulnerability exists in the Linux kernel's debugobjects component. Specifically, the function fill_pool() is called on RT (real-time) enabled kernels and ends up calling rtlock_lock(). If the current task is already blocked on another lock (indicated by current::pi_blocked_on being set), rtlock_lock() asserts because a task can only block on one lock at a time to avoid corruption of the priority inheritance chain. The vulnerability arises because fill_pool() did not check if current::pi_blocked_on was set before proceeding, potentially causing assertion failures and priority inheritance chain corruption.

The fix prevents this issue by expanding the conditional logic in fill_pool() to take current::pi_blocked_on into account, thereby avoiding calling rtlock_lock() when the current task is already blocked on a lock.

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Impact Analysis

This vulnerability can lead to assertion failures in the Linux kernel on real-time enabled systems, potentially causing system instability or crashes. Because the priority inheritance chain can become corrupted if a task blocks on multiple locks, this may affect the scheduling and real-time behavior of the system, leading to degraded performance or unexpected behavior in time-sensitive applications.

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