On Wed, 28 Aug 2013 14:39:53 +0800 Shaohua Li <shli@xxxxxxxxxx> wrote: > On Wed, Aug 28, 2013 at 02:32:52PM +1000, NeilBrown wrote: > > On Tue, 27 Aug 2013 16:53:30 +0800 Shaohua Li <shli@xxxxxxxxxx> wrote: > > > > > On Tue, Aug 27, 2013 at 01:17:52PM +1000, NeilBrown wrote: > > > > > > > > > Then get_active_stripe wouldn't need to worry about device_lock at all and > > > > would only need to get the hash lock for the particular sector. That should > > > > make it a lot simpler. > > > > > > did you mean get_active_stripe() doesn't need device_lock for any code path? > > > How could it be safe? device_lock still protects something like handle_list, > > > delayed_list, which release_stripe() will use while a get_active_stripe can run > > > concurrently. > > > > Yes you will still need device_lock to protect list_del_init(&sh->lru), > > as well as the hash lock. > > Do you need device_lock anywhere else in there? > > That's what I mean. So I need get both device_lock and hash_lock. To not > deadlock, I need release hash_lock and relock device_lock/hash_lock. Since I > release lock, I need recheck if I can find the stripe in hash again. So the > seqcount locking doesn't simplify things here. I thought the seqlock only fixes > one race. Did I miss anything? Can you order the locks so that you take the hash_lock first, then the device_lock? That would be a lot simpler. > > I saw your tree only has seqcount_write lock in one place, but there are still > other places which changing quiesce, degraded. I thought we still need lock all > locks like what I did. Can you be specific? I thought I had convinced my self that I covered everything that was necessary, but I might have missed something. NeilBrown
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