Messages in this thread Patch in this message | | | From | Ian Campbell <> | Date | Sun, 17 Aug 2008 17:19:32 +0100 | Subject | Re: kernel BUG at lib/radix-tree.c:473! |
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On Fri, 2008-08-15 at 01:00 +0100, Hugh Dickins wrote: > On Fri, 15 Aug 2008, Johannes Weiner wrote: > > Jeremy Fitzhardinge <jeremy@goop.org> writes: > > > Hugh Dickins wrote: > > > > > >> An additional useful input would be: what happens if you replace > > >> that /dev/fb0 by a symlink /dev/fb0 pointing to an fb0 device node in > > >> one of your disk filesystems? I rather expect that to cause the same > > >> trouble, which would argue that the driver is wrong and shmem right. > > > > > > I don't follow. Do you mean make /dev/fb0 a plain file on a > > > filesystem? Or make it a disk device node? Something else? > > > > Creating a device node on a different filesystem to see if the driver > > only worked with the safe shmem set_page_dirty and now breaks due to > > exposure to the generic version. Or if the driver works with the > > generic version through other mappings and the shmem code screws it up > > somewhere else. > > Yes, that's it. I think it was ext2 I referred to, when I worried > about this when making the change to tmpfs; and my reading of it > was that ext2 left a device node's a_ops unset, as I was changing > tmpfs to do. (Looking at it again, ext2 doesn't even specify its > .set_page_dirty, so even if it had assigned an a_ops, it wouldn't > have avoided the default behaviour.) But I'd like to hear what > actually happens in practice, rather than relying on my reading.
Creating /tmp/fb0 on an ext3 filesystem gives the same behaviour.
FWIW the patch below apparently makes it work for me, but I'm not going to pretend I follow what's going on, why or what else it breaks ;-)
Ian.
diff --git a/drivers/video/fb_defio.c b/drivers/video/fb_defio.c index 59df132..8414646 100644 --- a/drivers/video/fb_defio.c +++ b/drivers/video/fb_defio.c @@ -24,6 +24,10 @@ #include <linux/rmap.h> #include <linux/pagemap.h> +static const struct address_space_operations fb_defio_aops = { + .set_page_dirty = __set_page_dirty_no_writeback, +}; + /* this is to find and return the vmalloc-ed fb pages */ static int fb_deferred_io_fault(struct vm_area_struct *vma, struct vm_fault *vmf) @@ -119,6 +123,7 @@ static int fb_deferred_io_mmap(struct fb_info *info, struct vm_area_struct *vma) vma->vm_ops = &fb_deferred_io_vm_ops; vma->vm_flags |= ( VM_IO | VM_RESERVED | VM_DONTEXPAND ); vma->vm_private_data = info; + vma->vm_file->f_mapping->a_ops = &fb_defio_aops; return 0; } -- Ian Campbell
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