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) If yes, then the patch that I posted should be OK, because it wouldn't break this concurrency. 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. Mikulas
