** Also affects: ubuntu-z-systems
Importance: Undecided
Status: New
** Changed in: ubuntu-z-systems
Status: New => Triaged
** Changed in: ubuntu-z-systems
Importance: Undecided => High
** Changed in: ubuntu-z-systems
Assignee: (unassigned) => Canonical Kernel Team (canonical-kernel-team)
--
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:
Triaged
Status in linux package in Ubuntu:
New
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 : [email protected]
Unsubscribe : https://launchpad.net/~kernel-packages
More help : https://help.launchpad.net/ListHelp
