On Fri 13-12-19 19:26:17, John Hubbard wrote: > Add tracking of pages that were pinned via FOLL_PIN. > > As mentioned in the FOLL_PIN documentation, callers who effectively set > FOLL_PIN are required to ultimately free such pages via unpin_user_page(). > The effect is similar to FOLL_GET, and may be thought of as "FOLL_GET > for DIO and/or RDMA use". > > Pages that have been pinned via FOLL_PIN are identifiable via a > new function call: > > bool page_dma_pinned(struct page *page); > > What to do in response to encountering such a page, is left to later > patchsets. There is discussion about this in [1], [2], and [3]. > > This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). > > [1] Some slow progress on get_user_pages() (Apr 2, 2019): > https://lwn.net/Articles/784574/ > [2] DMA and get_user_pages() (LPC: Dec 12, 2018): > https://lwn.net/Articles/774411/ > [3] The trouble with get_user_pages() (Apr 30, 2018): > https://lwn.net/Articles/753027/ > > Suggested-by: Jan Kara <jack@xxxxxxx> > Suggested-by: Jérôme Glisse <jglisse@xxxxxxxxxx> > Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx> > --- > > Hi Jan, > > This should address all of your comments for patch 23! Thanks. One comment below: > @@ -1486,6 +1500,10 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma, > VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page); > if (flags & FOLL_TOUCH) > touch_pmd(vma, addr, pmd, flags); > + > + if (!try_grab_page(page, flags)) > + return ERR_PTR(-ENOMEM); > + > if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) { > /* > * We don't mlock() pte-mapped THPs. This way we can avoid I'd move this still a bit higher - just after VM_BUG_ON_PAGE() and before if (flags & FOLL_TOUCH) test. Because touch_pmd() can update page tables and we don't won't that if we're going to fail the fault. With this fixed, the patch looks good to me so you can then add: Reviewed-by: Jan Kara <jack@xxxxxxx> Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
