On Tue, Jun 20, 2017 at 11:10:56PM -0700, Hugh Dickins wrote: > On Wed, 21 Jun 2017, Willy Tarreau wrote: > > On Tue, Jun 20, 2017 at 10:49:16PM -0700, Hugh Dickins wrote: > > > On Mon, 19 Jun 2017, Greg Kroah-Hartman wrote: > > > > > > > 3.18-stable review patch. If anyone has any objections, please let me know. > > > > > > > > ------------------ > > > > > > > > From: Hugh Dickins <hughd@xxxxxxxxxx> > > > > > > > > commit 1be7107fbe18eed3e319a6c3e83c78254b693acb upstream. > > > > > > Here's a few adjustments to the 3.18 patch: no doubt you'll have > > > already sorted out any build errors (and I have to confess that > > > I haven't even tried to build this); and the VM_WARN_ON line (as > > > in 4.4) only fixes a highly unlikely error; but those FOLL_MLOCK > > > lines in mm/gup.c were mistaken, and do need to be deleted. > > > > Are you sure ? The test on the FOLL_MLOCK flag remains present in > > 4.11 and mainline : > > > > /* mlock all present pages, but do not fault in new pages */ > > if ((*flags & (FOLL_POPULATE | FOLL_MLOCK)) == FOLL_MLOCK) > > return -ENOENT; > > > > And this test was present although different in 3.18 as well : > > > > /* For mlock, just skip the stack guard page. */ > > if ((*flags & FOLL_MLOCK) && > > (stack_guard_page_start(vma, address) || > > stack_guard_page_end(vma, address + PAGE_SIZE))) > > > > So by removing it we're totally removing any test on FOLL_MLOCK. That > > might be the correct fix, but I'm just a bit surprized since the mainline > > patch doesn't remove it, and only removes the test on FOLL_POPULATE. > > I think I'm sure :) Please take another look, the intention of those > two FOLL_MLOCK tests is completely different. One of them is about > the mlock2() syscall (I think), which wants not to fault in every > page at syscall time; and the other is about stack guard pages > bogusly included in the vma extents, which must not be faulted in. > The stack guard pages are no longer included in the vma extents, > so we can just delete those lines (note the "&&" in the condition); > but we don't want mlock() to stop faulting its pages in. > > Makes sense now, or am I tired and confused? Your explanation sounds pretty fine to me, so I agree with you :-) Thanks! Willy