Re: [GIT PULL] Btrfs

Heiko Carstens
2013-11-15T14:58:53Z

On Fri, Nov 15, 2013 at 02:42:08PM +0100, Geert Uytterhoeven wrote:
> On Fri, Nov 15, 2013 at 2:40 PM, Chris Mason <chris.mason@fusionio.com> wrote:
> > Quoting Chris Mason (2013-11-15 07:21:31)
> >> Quoting Heiko Carstens (2013-11-15 06:32:16)
> >> > On Thu, Nov 14, 2013 at 12:19:52PM -0500, Chris Mason wrote:
> >> > > Hi Linus,
> >> > >
> >> > > Please pull my for-linus branch:
> >> > >
> >> > > git://git.kernel.org/pub/scm/linux/kernel/git/mason/linux-btrfs.git for-linus
> >> > >
> >> > > This is our usual merge window set of bug fixes, performance
> >> > > improvements and cleanups. Miao Xie has some really nice optimizations
> >> > > for writeback.
> >> > >
> >> > > Josef also expanded our sanity checks quite a bit; these make up a big
> >> > > chunk of the new lines.
> >> >
> >> > Hmm.. b19e68439375 "btrfs: Remove redundant local zero structure" seems to
> >> > use the empty_zero_page incorrectly and causes this compile warning on s390:
> >> >
> >> > CC fs/btrfs/ioctl.o
> >> > fs/btrfs/ioctl.c: In function 'btrfs_is_empty_uuid':
> >> > fs/btrfs/ioctl.c:372:2: warning: passing argument 2 of 'memcmp' makes pointer from
> >> > integer without a cast [enabled by default]
> >> > return !memcmp(uuid, empty_zero_page, BTRFS_UUID_SIZE);
> >> > ^
> >> >
> >> > In fact there seem to be two more incorrect usages in the kernel. The patch
> >> > below is not really tested.
> >>
> >> Thanks Heiko,
> >>
> >> I'll make a new pull with the btrfs part of this.
> >
> > Or something slightly different ;)
> >
> > BUG: unable to handle kernel paging request at 0000000001ba6000
> > IP: [<ffffffff812b3656>] memcmp+0xf/0x22
>
> I was just going to comment that
>
> + const void *zero_page = (const void *) page_to_phys(ZERO_PAGE(0));
>
> won't fly. You can't just cast a physical address to "void *".

Ouch.. I think that only works on s390 because we have a 1:1 mapping for
physical to virtual addresses in kernel space due to our split address spaces.

So for btrfs and kvm it should be page_to_virt(), and for the dma_map_single()
case I have no idea. :)