September 13-16, 2022
Dublin, Ireland + Virtual
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Friday, September 16 • 15:55 - 16:35
What Lockdep Does and Doesn't - Byungchul Park, LG Electronics

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Lockdep tracks lock acquisition order to detect deadlock, and IRQ and IRQ enable/disable state as well to take accident acquisitions into account. It should be turned off once it detects and reports a deadlock since the data structure and algorithm are not reusable after detection because of the complex design. Waits and their events that are never reachable eventually cause a deadlock. However, Lockdep is only interested in lock acquisition order, forcing to emulate lock acqusition even for waits and events that have nothing to do with real lock. Even worse, no one likes Lockdep's false positive detection because that prevents further one that might be more valuable. Which makes the kernel developers more sensitive to Lockdep's false positives. Besides those, by tracking lock acquisition order, it cannot correctly deal with read lock and cross-event e.g. wait_for_completion()/complete() for deadlock detection. Lockdep is no longer a good tool for the general purpose. Again, waits and their events that are never reachable eventually cause a deadlock. The new solution, Dept(DEPendency Tracker), focuses on waits and events themselves. Dept tracks waits and events and report it once it detects some events are never reachable.

avatar for Byungchul Park

Byungchul Park

Linux Kernel Developer, LG Electronics

Friday September 16, 2022 15:55 - 16:35 IST
Liffey Hall 1 (Level 1)
  Embedded Linux Conference (ELC)