On Sat, Oct 8, 2022 at 1:12 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote: > > On Sat, Oct 08, 2022, Hao Peng wrote: > > From: Peng Hao <flyingpeng@xxxxxxxxxxx> > > > > Synchronization operations on the writer side of SRCU should be > > invoked within the mutex. > > Why? Synchronizing SRCU is necessary only to ensure that all previous readers go > away before the old filter is freed. There's no need to serialize synchronization > between writers. The mutex ensures each writer operates on the "new" filter that's > set by the previous writer, i.e. there's no danger of a double-free. And the next > writer will wait for readers to _its_ "new" filter. > Array srcu_lock_count/srcu_unlock_count[] in srcu_data, which is used alternately to determine which readers need to wait to get out of the critical area. If two synchronize_srcu are initiated concurrently, there may be a problem with the judgment of gp. But if it is confirmed that there will be no writer concurrency, it is not necessary to ensure that synchronize_srcu is executed within the scope of the mutex lock. Thanks. > I think it's a moot point though, as this is a subset of patch I posted[*] to fix > other issues with the PMU event filter. > > [*] https://lore.kernel.org/all/20220923001355.3741194-2-seanjc@xxxxxxxxxx
