On Fri, Oct 18, 2024 at 12:58:09PM +0200, Christian König wrote: > Am 17.10.24 um 18:43 schrieb Rodrigo Vivi: > > On Thu, Oct 17, 2024 at 09:59:10AM +0200, Christian König wrote: > > > > > Purpose of this implementation is to provide drivers a generic way to > > > > > recover with the help of userspace intervention. Different drivers may > > > > > have different ideas of a "wedged device" depending on their hardware > > > > > implementation, and hence the vendor agnostic nature of the event. > > > > > It is up to the drivers to decide when they see the need for recovery > > > > > and how they want to recover from the available methods. > > > > > > > > > > Current implementation defines three recovery methods, out of which, > > > > > drivers can choose to support any one or multiple of them. Preferred > > > > > recovery method will be sent in the uevent environment as WEDGED=<method>. > > > > > Userspace consumers (sysadmin) can define udev rules to parse this event > > > > > and take respective action to recover the device. > > > > > > > > > > =============== ================================== > > > > > Recovery method Consumer expectations > > > > > =============== ================================== > > > > > rebind unbind + rebind driver > > > > > bus-reset unbind + reset bus device + rebind > > > > > reboot reboot system > > > > > =============== ================================== > > > Well that sounds like userspace would need to be involved in recovery. > > > > > > That in turn is a complete no-go since we at least need to signal all > > > dma_fences to unblock the kernel. In other words things like bus reset needs > > > to happen inside the kernel and *not* in userspace. > > > > > > What we can do is to signal to userspace: Hey a bus reset of device X > > > happened, maybe restart container, daemon, whatever service which was using > > > this device. > > Well, when we declare device 'wedged' it is because we don't want to take > > any drastic measures inside the kernel and want to leave it in a protected > > and unusable state. In a way that users wouldn't lose display for instance, > > or at least the device is in a debugable state. > > Uff, that needs to be very very well documented or otherwise the whole > approach is an absolutely clear NAK from my side as DMA-buf maintainer. > > > > > Then, the instructions here is to tell what could possibly be attempted > > from userspace to get the device to an usable state. > > > > The 'wedge' mode (the one emiting this uevent) needs to be responsible > > for signaling all the fences and everything needed for a clean unbind > > and whatever next step might be indicated to userspace. > > > > That should already be part of any wedged mode, regardless the uevent > > to inform the userspace here. > > You need to approach that from a different side. With the current patch set > you are ignoring documented mandatory driver behavior as far as I can see. > > So first of all describe in the documentation what the wedged mode is and > what requirements a driver has to fulfill to enter it: > https://docs.kernel.org/gpu/drm-uapi.html#device-reset > > Especially document that all system memory accesses of the device needs to > be blocked by (for example) disabling DMA accesses in the PCI config space. > > When it is guaranteed that the device can't access any system memory any > more the device driver should signal all pending fences of this device. > > And only after all of that is done the driver can send an uevent to inform > userspace that it can debug the hanged state. Sure, will do. > As far as I can see this makes the enum how to recover the device > superfluous because you will most likely always need a bus reset to get out > of this again. That depends on the kind of fault the device has encountered and the bus it is sitting on. There could be buses that don't support reset. Raag
