On Mon, Feb 26, 2024 at 03:38:55PM -1000, Tejun Heo wrote: > Boqun pointed out that workqueues aren't handling BH work items on offlined > CPUs. Unlike tasklet which transfers out the pending tasks from > CPUHP_SOFTIRQ_DEAD, BH workqueue would just leave them pending which is > problematic. Note that this behavior is specific to BH workqueues as the > non-BH per-CPU workers just become unbound when the CPU goes offline. > > This patch fixes the issue by draining the pending BH work items from an > offlined CPU from CPUHP_SOFTIRQ_DEAD. Because work items carry more context, > it's not as easy to transfer the pending work items from one pool to > another. Instead, run BH work items which execute the offlined pools on an > online CPU. > > Note that this assumes that no further BH work items will be queued on the > offlined CPUs. This assumption is shared with tasklet and should be fine for > conversions. However, this issue also exists for per-CPU workqueues which > will just keep executing work items queued after CPU offline on unbound > workers and workqueue should reject per-CPU and BH work items queued on > offline CPUs. This will be addressed separately later. > > Signed-off-by: Tejun Heo <tj@xxxxxxxxxx> > Reported-by: Boqun Feng <boqun.feng@xxxxxxxxx> > Link: http://lkml.kernel.org/r/Zdvw0HdSXcU3JZ4g@boqun-archlinux Applying this to wq/for-6.9. Thanks. -- tejun
