On 9/17/19 12:23 PM, David Rientjes wrote: > On Mon, 16 Sep 2019, David Rientjes wrote: > >> Brijesh and Tom, we currently hit this any time we boot an SEV enabled >> Ubuntu 18.04 guest; I assume that guest kernels, especially those of such >> major distributions, are expected to work with warnings and BUGs when >> certain drivers are enabled. >> >> If the vmap purge lock is to remain a mutex (any other reason that >> unmapping aliases can block?) then it appears that allocating a dmapool >> is the only alternative. Is this something that you'll be addressing >> generically or do we need to get buy-in from the maintainers of this >> specific driver? >> > > We've found that the following applied on top of 5.2.14 suppresses the > warnings. > > Christoph, Keith, Jens, is this something that we could do for the nvme > driver? I'll happily propose it formally if it would be acceptable.
No, this is not going to be acceptable, I'm afraid. This tells blk-mq that the driver always needs blocking context for queueing IO, which will increase latencies for the cases where we'd otherwise issue IO directly from the context that queues it. -- Jens Axboe
