Public bug reported: Description: kernel: fix rwlock implementation Symptom: Kernel hangs, due to deadlock on an rwlock. Problem: With upstream commit 94232a4332de ("s390/rwlock: improve writer fairness") rwlock writer fairness was supposed to be implemented. If a writer tries to take an rwlock it sets unconditionally the writer bit within the lock word and waits until all readers have released the lock. This however can lead to a deadlock since rwlocks can be taken recursively by readers. If e.g. CPU 0 holds the lock as a reader, and CPU 1 wants to write-lock the lock, then CPU 1 sets the writer bit and afterwards busy waits for CPU 0 to release the lock. If now CPU 0 tries to read-lock the lock again (recursively) it will also busy wait until CPU 1 removes the writer bit, which will never happen, since it waits for the first reader on CPU 0 to release the lock. Solution: Revert the rwlock writer fairness semantics again.
** Affects: ubuntu-z-systems Importance: High Assignee: Canonical Kernel Team (canonical-kernel-team) Status: Triaged ** Affects: linux (Ubuntu) Importance: Undecided Assignee: Skipper Bug Screeners (skipper-screen-team) Status: New ** Tags: architecture-s39064 bugnameltc-166421 severity-high targetmilestone-inin16041 ** Tags added: architecture-s39064 bugnameltc-166421 severity-high targetmilestone-inin16041 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1761674 Title: [Ubuntu 16.04] kernel: fix rwlock implementation To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu-z-systems/+bug/1761674/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs