Messages in this thread | | | Date | Tue, 5 Sep 2017 15:36:11 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH 0/2] smp/hotplug annotations |
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On Tue, 5 Sep 2017, Thomas Gleixner wrote: > On Tue, 5 Sep 2017, Peter Zijlstra wrote: > > > These two patches appear to make hotplug work again without tripping lockdep. > > They cover the case where the plug/unplug succeeds, but they will not work > when a plug/unplug operation fails, because after a fail it rolls back > automatically, so in case UP fails, it will go down again, but the > initiator side still waits on the 'UP' completion. Same issue on down. > > I think that extra lockdep magic can be avoided completely by splitting the > completions into a 'up' and a 'down' completion, but that only solves a > part of the problem. The current failure handling does an automated > rollback, so if UP fails somewhere the AP rolls back, which means it > invokes the down callbacks. DOWN the other way round. > > We can solve that by changing the way how rollback is handled so it does > not automatically roll back. > > if (callback() < 0) { > store_state(); > complete(UP); > wait_for_being_kicked_again() > } > > and on the control side have > > wait_for_completion(UP); > > if (UP->failed) { > kick(DOWN); > wait_for_completion(DOWN); > } > > It's not entirely trivial, but I haven't seen a real problem with it yet.
Now I found one. It's the multi instance rollback. This is a nested rollback mechanism deep in the call chain. Seperating that one is going to be a major pain.
Thanks,
tglx
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