On Sun, May 13, 2018 at 02:59:50PM +0200, Jaromr Dole?ek wrote: > 2018-05-12 21:24 GMT+02:00 Chuck Silvers <c...@chuq.com>: > > the problem with keeping the pages locked (ie. PG_BUSY) while accessing > > the user address space is that it can lead to deadlock if the page > > we are accessing via the kernel mapping is the same page that we are > > accessing via the user mapping. > > The pages marked PG_BUSY for the UBC transfer are part of page cache. > I sincerely hope it's impossible to have any user mapping for it.
the whole point of UBC is that the pages caching the data used by read/write are the same pages used by mmap. that's how we avoid the double-caching and cache coherency problems that the pre-UBC scheme had. so yes, these pages can have user mappings at the same time as they are mapped in the kernel. -Chuck