On Thu, Feb 17, 2022 at 11:08:38PM -0500, Theodore Ts'o wrote: > On Thu, Feb 17, 2022 at 05:06:45PM -0800, John Hubbard wrote: > > Yes. And looking at the pair of backtraces below, this looks very much > > like another aspect of the "get_user_pages problem" [1], originally > > described in Jan Kara's 2018 email [2]. > > Hmm... I just posted my analysis, which tracks with yours; but I had > forgotten about Jan's 2018 e-mail on the matter. > > > I'm getting close to posting an RFC for the direct IO conversion to > > FOLL_PIN, but even after that, various parts of the kernel (reclaim, > > filesystems/block layer) still need to be changed so as to use > > page_maybe_dma_pinned() to help avoid this problem. There's a bit > > more than that, actually. > > The challenge is that fixing this "the right away" is probably not > something we can backport into an LTS kernel, whether it's 5.15 or > 5.10... or 4.19. Don't worry about stable backports to start with. Do it the "right way" first and then we can consider if it needs to be backported or not. thanks, greg k-h
