On Fri, Sep 25, 2020 at 12:56:05PM -0700, Linus Torvalds wrote: > So I think we can simply add a > > if (page_mapcount(page) != 1) > return false; > > to page_maybe_dma_pinned(), and that very naturally protects against > the "is the page count perhaps elevated due to a lot of forking?" How about the MAP_SHARED case where the page is pinned by some process but also shared (so mapcount can be >1)? > And honestly, since this is all getting fairly late in the rc, and it > took longer than I thought, I think we should do the GFP_ATOMIC > approach for now - not great, but since it only triggers for this case > that really should never happen anyway, I think it's probably the best > thing for 5.9, and we can improve on things later. Sorry for that. Maybe I should have moved even faster. Would the ATOMIC version always work? I mean, I thought it could fail anytime, so any fork() can start to fail for the tests too. PS. I do plan to post a GFP_KERNEL version soon today, no matter for this release or the next one. -- Peter Xu
