On Tue, Nov 17, 2015 at 12:16:03PM -0800, Dan Williams wrote: > While dax pmd mappings are functional in the nominal path they trigger > kernel crashes in the following paths: > > BUG: unable to handle kernel paging request at ffffea0004098000 > IP: [<ffffffff812362f7>] follow_trans_huge_pmd+0x117/0x3b0 > [..] > Call Trace: > [<ffffffff811f6573>] follow_page_mask+0x2d3/0x380 > [<ffffffff811f6708>] __get_user_pages+0xe8/0x6f0 > [<ffffffff811f7045>] get_user_pages_unlocked+0x165/0x1e0 > [<ffffffff8106f5b1>] get_user_pages_fast+0xa1/0x1b0 > > kernel BUG at arch/x86/mm/gup.c:131! > [..] > Call Trace: > [<ffffffff8106f34c>] gup_pud_range+0x1bc/0x220 > [<ffffffff8106f634>] get_user_pages_fast+0x124/0x1b0 > > BUG: unable to handle kernel paging request at ffffea0004088000 > IP: [<ffffffff81235f49>] copy_huge_pmd+0x159/0x350 > [..] > Call Trace: > [<ffffffff811fad3c>] copy_page_range+0x34c/0x9f0 > [<ffffffff810a0daf>] copy_process+0x1b7f/0x1e10 > [<ffffffff810a11c1>] _do_fork+0x91/0x590 > > All of these paths are interpreting a dax pmd mapping as a transparent > huge page and making the assumption that the pfn is covered by the > memmap, i.e. that the pfn has an associated struct page. PTE mappings > do not suffer the same fate since they have the _PAGE_SPECIAL flag to > cause the gup path to fault. We can do something similar for the PMD > path, or otherwise defer pmd support for cases where a struct page is > available. For now, 4.4-rc and -stable need to disable dax pmd support > by default. > > For development the "depends on BROKEN" line can be removed from > CONFIG_FS_DAX_PMD. > > Cc: <stable@xxxxxxxxxxxxxxx> > Cc: Jan Kara <jack@xxxxxxxx> > Cc: Dave Chinner <david@xxxxxxxxxxxxx> > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxxxx> > Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > Reported-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> > Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> Acked-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
