On Tue, Mar 20, 2018 at 12:45 AM, Tejun Heo <t...@kernel.org> wrote: > Hello, Lai. > > On Fri, Mar 16, 2018 at 02:01:35PM +0800, Lai Jiangshan wrote: >> > +bool flush_rcu_work(struct rcu_work *rwork) >> > +{ >> > + if (test_bit(WORK_STRUCT_PENDING_BIT, >> > work_data_bits(&rwork->work))) { >> > + rcu_barrier(); >> > + flush_work(&rwork->work); >> > + return true; >> >> A possible tiny improvement: check if it was already queued on wq. >> For example: >> >> if (test_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&rwork->work))) { >> if (!flush_work(&rwork->work)) { >> rcu_barrier(); >> flush_work(&rwork->work); >> } >> return true; > > But this breaks the guarantee that flush_work waits for the latest > queueing instance. Please consider the following scenario.
Oh, I'm sorry I was wrong. It is so evident that "flush_work(&rwork->work) return true" doesn't equals to "it has been queued on wq". To detect if "it has been queued on wq" requires a bunch of code. It is not worthy to complicate this function. > > > 1. rcu-work is queued > 2. rcu-work starts executing > 3. rcu-work is queued again > 4. rcu-work is flushed > 5. execution finishes > 6. flush finishes > 7. execution finishes > > 6 should happen after 7 but it didn't. > > Thanks. > > -- > tejun