On Thu, Apr 20, 2017 at 02:46:51PM -0700, Dan Williams wrote: > On Sat, Mar 18, 2017 at 2:52 AM, tip-bot for Kirill A. Shutemov > <[email protected]> wrote: > > Commit-ID: 2947ba054a4dabbd82848728d765346886050029 > > Gitweb: > > http://git.kernel.org/tip/2947ba054a4dabbd82848728d765346886050029 > > Author: Kirill A. Shutemov <[email protected]> > > AuthorDate: Fri, 17 Mar 2017 00:39:06 +0300 > > Committer: Ingo Molnar <[email protected]> > > CommitDate: Sat, 18 Mar 2017 09:48:03 +0100 > > > > x86/mm/gup: Switch GUP to the generic get_user_page_fast() implementation > > > > This patch provides all required callbacks required by the generic > > get_user_pages_fast() code and switches x86 over - and removes > > the platform specific implementation. > > > > Signed-off-by: Kirill A. Shutemov <[email protected]> > > Cc: Andrew Morton <[email protected]> > > Cc: Aneesh Kumar K . V <[email protected]> > > Cc: Borislav Petkov <[email protected]> > > Cc: Catalin Marinas <[email protected]> > > Cc: Dann Frazier <[email protected]> > > Cc: Dave Hansen <[email protected]> > > Cc: H. Peter Anvin <[email protected]> > > Cc: Linus Torvalds <[email protected]> > > Cc: Peter Zijlstra <[email protected]> > > Cc: Rik van Riel <[email protected]> > > Cc: Steve Capper <[email protected]> > > Cc: Thomas Gleixner <[email protected]> > > Cc: [email protected] > > Cc: [email protected] > > Link: > > http://lkml.kernel.org/r/[email protected] > > [ Minor readability edits. ] > > Signed-off-by: Ingo Molnar <[email protected]> > > I'm still trying to spot the bug, but bisect points to this patch as > the point at which my unit tests start failing with the following > signature: > > [ 35.423841] WARNING: CPU: 8 PID: 245 at lib/percpu-refcount.c:155 > percpu_ref_switch_to_atomic_rcu+0x1f5/0x200
Okay, I've tracked it down. The issue is triggered by replacment get_page() with page_cache_get_speculative(). page_cache_get_speculative() doesn't have get_zone_device_page(). :-| And I think it's your bug, Dan: it's wrong to have get_/put_zone_device_page() in get_/put_page(). I must be handled by page_ref_* machinery to catch all cases where we manipulate with page refcount. Back to the big picture: I hate that we need to have such additional code in page refcount primitives. I worked hard to remove compound page ugliness from there and now zone_device creeping in... Is it the only option? -- Kirill A. Shutemov
