On Fri 15-06-18 14:06:20, Jan Kara wrote: > On Wed 13-06-18 07:33:15, Tejun Heo wrote: > > Hello, Jan. > > > > On Tue, Jun 12, 2018 at 05:57:54PM +0200, Jan Kara wrote: > > > > Yeah, right, so the root cause is that we're walking the wb_list while > > > > holding lock and expecting the object to stay there even after lock is > > > > released. Hmm... we can use a mutex to synchronize the two > > > > destruction paths. It's not like they're hot paths anyway. > > > > > > Hmm, do you mean like having a per-bdi or even a global mutex that would > > > protect whole wb_shutdown()? Yes, that should work and we could get rid of > > > WB_shutting_down bit as well with that. Just it seems a bit strange to > > > > Yeap. > > > > > introduce a mutex only to synchronize these two shutdown paths - usually > > > locks protect data structures and in this case we have cgwb_lock for > > > that so it looks like a duplication from a first look. > > > > Yeah, I feel a bit reluctant too but I think that's the right thing to > > do here. This is an inherently weird case where there are two ways > > that an object can go away with the immediate drain requirement from > > one side. It's not a hot path and the dumber the synchronization the > > better, right? > > Yeah, fair enough. Something like attached patch? It is indeed considerably > simpler than fixing synchronization using WB_shutting_down. This one even > got some testing using scsi_debug, I want to do more testing next week with > more cgroup writeback included. OK, the test has passed some beating with cgroup writeback running. I'll do official posting shortly. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
