search for: invalidate_start_rang

...ever win against copy_from_user using mmu_notifiers? The synchronization requirements are likely always more expensive unless large and scattered copies are being done.. The rcu is about the only simple approach that could be less expensive, and that gets back to the question if you can block an invalidate_start_range in synchronize_rcu or not.. So, frankly, I'd revert it until someone could prove the rcu solution is OK.. BTW, how do you get copy_from_user to work outside a syscall? Also, why can't this just permanently GUP the pages? In fact, where does it put_page them anyhow? Worrying that 7f466 a...

...ever win against copy_from_user using mmu_notifiers? The synchronization requirements are likely always more expensive unless large and scattered copies are being done.. The rcu is about the only simple approach that could be less expensive, and that gets back to the question if you can block an invalidate_start_range in synchronize_rcu or not.. So, frankly, I'd revert it until someone could prove the rcu solution is OK.. BTW, how do you get copy_from_user to work outside a syscall? Also, why can't this just permanently GUP the pages? In fact, where does it put_page them anyhow? Worrying that 7f466 a...

...correct mmu is active. > The synchronization requirements are likely always > more expensive unless large and scattered copies are being done.. > > The rcu is about the only simple approach that could be less > expensive, and that gets back to the question if you can block an > invalidate_start_range in synchronize_rcu or not.. > > So, frankly, I'd revert it until someone could prove the rcu solution is > OK.. I have it all disabled at compile time, so reverting isn't urgent anymore. I'll wait a couple more days to decide what's cleanest. > BTW, how do you get co...

On Fri, Aug 02, 2019 at 05:40:07PM +0800, Jason Wang wrote: > > This must be a proper barrier, like a spinlock, mutex, or > > synchronize_rcu. > > > I start with synchronize_rcu() but both you and Michael raise some > concern. I've also idly wondered if calling synchronize_rcu() under the various mm locks is a deadlock situation. > Then I try spinlock and mutex:

On Fri, Aug 02, 2019 at 05:40:07PM +0800, Jason Wang wrote: > > This must be a proper barrier, like a spinlock, mutex, or > > synchronize_rcu. > > > I start with synchronize_rcu() but both you and Michael raise some > concern. I've also idly wondered if calling synchronize_rcu() under the various mm locks is a deadlock situation. > Then I try spinlock and mutex: