On Thu, Feb 29, 2024 at 10:37:28AM -1000, Tejun Heo wrote: > 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. > FWIW, Reviewed-by: Boqun Feng <boqun.feng@xxxxxxxxx> (I took a look yesterday, but hasn't gotten the time to reply..) Regards, Boqun > Thanks. > > -- > tejun
