------- Comment From h.carst...@de.ibm.com 2018-04-14 06:40 EDT------- (In reply to comment #14) > I built a 16.04(4.4 based kenrel) with the requested patch. > > The test kernel can be downloaded from: > http://kernel.ubuntu.com/~jsalisbury/lp1761674/xenial > > Can you test this kernel and see if it resolves this bug? > > Note, to test this kernel, you need to install both the linux-image and > linux-image-extra .deb packages.
The bug is close to impossible to reproduce, since it's a hard to hit race. So I could only verify that the kernel/system still boots and did some basic tests - which all passed. ------- Comment From h.carst...@de.ibm.com 2018-04-14 06:43 EDT------- (In reply to comment #14) > I also tried to apply this patch to the 4.13 based 17.10 Artful kernel. > However, I'll have to perform allot of back porting for Artful. For > example, the patch relies on _raw_compare_and_swap(). However, this > function was removed in v4.12-rc1 by commit 02c503f. Can you confirm this > patch is needed in Artful, and if you recommend any prereq patches? Yes, the bug is also present in v4.13. I attached a kernel patch agains vanilla v4.13 that is supposed to fix the bug for this kernel version as well. ** Tags removed: bugnameltc-166421 kernel-da-key severity-high -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1761674 Title: [Ubuntu 16.04] kernel: fix rwlock implementation Status in Ubuntu on IBM z Systems: In Progress Status in linux package in Ubuntu: Fix Released Status in linux source package in Xenial: In Progress Status in linux source package in Artful: Incomplete Status in linux source package in Bionic: Fix Released Bug description: 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. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu-z-systems/+bug/1761674/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
