On Sat, Apr 26, 2025 at 07:14:54PM +0200, Danilo Krummrich wrote: > On Sat, Apr 26, 2025 at 10:09:39AM -0700, Boqun Feng wrote: > > On Sat, Apr 26, 2025 at 03:30:38PM +0200, Danilo Krummrich wrote: > > > This patch series implements a direct accessor for the data stored within > > > a Devres container for cases where we can proof that we own a reference > > > to a Device<Bound> (i.e. a bound device) of the same device that was used > > > to create the corresponding Devres container. > > > > > > Usually, when accessing the data stored within a Devres container, it is > > > not clear whether the data has been revoked already due to the device > > > being unbound and, hence, we have to try whether the access is possible > > > and subsequently keep holding the RCU read lock for the duration of the > > > access. > > > > > > However, when we can proof that we hold a reference to Device<Bound> > > > matching the device the Devres container has been created with, we can > > > guarantee that the device is not unbound for the duration of the > > > lifetime of the Device<Bound> reference and, hence, it is not possible > > > for the data within the Devres container to be revoked. > > > > > > Therefore, in this case, we can bypass the atomic check and the RCU read > > > lock, which is a great optimization and simplification for drivers. > > > > > > > Nice! However, IIUC, if the users use Devres::new() to create a `Devres` > > , they will have a `Devres` they can revoke anytime, which means you can > > still revoke the `Devres` even if the device is bound. > > No, a user of Devres can't revoke the inner Revocable itself. A user can only > drop the Devres instance, in which case the user also wouldn't be able to call > access_with() anymore. > Oh, right, because it's a `Devres` not `Revocable` in general. > > Also if a `Devres` belongs to device A, but someone passes device B's > > bound reference to `access_with()`, the compiler won't check for that, > > and the `Devres` can be being revoked as the same, no? If so the > > function is not safe. > > Devres::access_with() compares the Device<Bound> parameter with its inner > ARef<Device>, and just fails if they don't match. I see, I missed that. Thanks! Regards, Boqun
