On Tue, Apr 24, 2018 at 06:18:54PM -0400, Mikulas Patocka wrote: > > > On Sat, 21 Apr 2018, Keith Busch wrote: > > > On Sat, Apr 21, 2018 at 09:59:48AM -0400, Mikulas Patocka wrote: > > > > > There's a bug in the nvme block device driver that causes failure when we > > > have no initramfs and the root filesystem is directly on nvme. The driver > > > spawns a work item nvme_reset_work() in the nvme_wq workqueue, but doesn't > > > wait for it. The result is that the kernel attempts to mount the root > > > filesystem before nvme_reset_work() finishes and it panics because it > > > can't find the root device. > > > > > > It can be fixed with this simple patch (perhaps you can come up with a > > > better patch that uses the asynchronous probing infrastructure?) > > > > We probe asynchronously to fix other issues. > > > > First is that boot takes way > > too long if you have a lot of devices when probing all of them serially, > > and then certain init systems kill the probe task after a certain time, > > breaking boot for those. > > > > Is there something we can do for your setup to have the kernel wait for > > the root partition to be available instead of givinig up after pci probe? > > Are different PCI NVME devices probed concurrently by the PCI API? (I > can't try, I have just one) It does not. > If yes, then the patch that I posted should be > OK, because it wouldn't break this concurrency. But you're waiting for the wrong work queue: the driver's reset_work won't get your root filesystem. That is handled in the scan_work. > If not, then you need to make sure that wait_for_device_probe() waits for > the NVME probe to finish. The kernel calls wait_for_device_probe() just > before it attempts to mount the root filesystem. I don't know which of the > kernel frameworks would be best suited to accomplish that. Perhaps the > simplest solution would be to increment probe_count in nvme_probe and > decrement it when the probe work item finishes - but it is not exported > and you'd need to create helper functions in drivers/base/dd.c to do that. Will have to look into it, but I think an async_domain is going to be the right way to go and shouldn't require any changes outside nvme.
