On Thu, Dec 7, 2023 at 8:12 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, Dec 07, 2023 at 07:59:03PM +0800, Yafang Shao wrote: > > On Thu, Dec 7, 2023 at 6:19 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > On Wed, Dec 06, 2023 at 10:08:40PM +0800, Yafang Shao wrote: > > > > On Wed, Dec 6, 2023 at 9:31 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > > > On Wed, Dec 06, 2023 at 11:53:55AM +0000, Yafang Shao wrote: > > > > > > After upgrading our kernel from version 4.19 to 6.1, certain regressions > > > > > > occurred due to the driver's asynchronous probe behavior. Specifically, > > > > > > the SCSI driver transitioned to an asynchronous probe by default, resulting > > > > > > in a non-fixed root disk behavior. In the prior 4.19 kernel, the root disk > > > > > > was consistently identified as /dev/sda. However, with kernel 6.1, the root > > > > > > disk can be any of /dev/sdX, leading to issues for applications reliant on > > > > > > /dev/sda, notably impacting monitoring systems monitoring the root disk. > > > > > > > > > > Device names are never guaranteed to be stable, ALWAYS use a persistant > > > > > names like a filesystem label or other ways. Look at /dev/disk/ for the > > > > > needed ways to do this properly. > > > > > > > > The root disk is typically identified as /dev/sda or /dev/vda, right? > > > > > > Depends on your system. It can also be identified, in the proper way, > > > as /dev/disk/by-uuid/eef0abc1-4039-4c3f-a123-81fc99999993 if you want > > > (note, fake uuid, use your own disk uuid please.) > > > > > > Why not do that? That's the most stable and recommended way of doing > > > things. > > > > Adapting to this change isn't straightforward, especially for a large > > fleet of servers. Our monitoring system needs to accommodate and > > adjust accordingly. > > Agreed, that can be rough. But as this is an issue that was caused by a > scsi core change, perhaps the scsi developers can describe why it's ok. > > But really, device naming has ALWAYS been known to not be > deterministic, which is why Pat and I did all the driver core work 20+ > years ago so that you have the ability to properly name your devices in > a way that is deterministic. Using the kernel name like sda is NOT > using that functionality, so while it has been nice to see that it has > been stable for you for a while, you are playing with fire here and will > get burned one day when the firmware in your devices decide to change > response times. I agree that using UUID is a better approach. However, it's worth noting that the widely used IO monitoring tool 'iostat' faces challenges when working with UUIDs. This indicates that there's a significant amount of work ahead of us in this aspect. > > > > > While reverting to synchronous probing could ensure > > > > stability, it's worth noting that asynchronous probing can potentially > > > > shorten the reboot duration under specific conditions. Thus, there > > > > might be some resistance to reverting this change as it offers > > > > performance benefits in certain scenarios. That's why I prefer to > > > > introduce a kernel parameter for it. > > > > > > I don't want to add a new parameter that we need to support for forever > > > and add to the complexity of the system unless it is REALLY needed. > > > > BTW, since there's already a 'driver_async_probe=', introducing > > another 'driver_sync_probe=' wouldn't significantly increase the > > maintenance overhead. > > Any new code adds maintenance overhead and complexity, so you have to > justify it's existance especially when you are not going to be the one > maintaining it :) Understood. -- Regards Yafang
