On Tue, 4 Jun 2019 at 11:03, Yuyang Du <duyuy...@gmail.com> wrote: > > Hi Waiman, > > On Tue, 21 May 2019 at 05:01, Waiman Long <long...@redhat.com> wrote: > > > > Because of writer lock stealing, it is possible that a constant > > stream of incoming writers will cause a waiting writer or reader to > > wait indefinitely leading to lock starvation. > > > > This patch implements a lock handoff mechanism to disable lock stealing > > and force lock handoff to the first waiter or waiters (for readers) > > in the queue after at least a 4ms waiting period unless it is a RT > > writer task which doesn't need to wait. The waiting period is used to > > avoid discouraging lock stealing too much to affect performance. > > I was working on a patchset to solve read-write lock deadlock > detection problem (https://lkml.org/lkml/2019/5/16/93). > > One of the mistakes in that work is that I considered the following > case as deadlock:
Sorry everyone, but let me rephrase: One of the mistakes in that work is that I considered the following case as no deadlock: > > T1 T2 > -- -- > > down_read1 down_write2 > > down_write2 down_read1 > > So I was trying to understand what really went wrong and find the > problem is that if I understand correctly the current rwsem design > isn't showing real fairness but priority in favor of write locks, and > thus one of the bad effects is that read locks can be starved if write > locks keep coming. > > Luckily, I noticed you are revamping rwsem and seem to have thought > about it already. I am not crystal sure what is your work's > ramification on the above case, so hope that you can shed some light > and perhaps share your thoughts on this. > > Thanks, > Yuyang
