On Thu 07-01-16 22:27:51, Ross Zwisler wrote:
> In __dax_pmd_fault() we currently assume that get_block() will always set
> bh.b_bdev and we unconditionally dereference it in __dax_dbg(). This
> assumption isn't always true - when called for reads of holes
> ext4_dax_mmap_get_block() returns a buffer head where bh->b_bdev is never
> set. I hit this BUG while testing the DAX PMD fault path.
>
> Instead, initialize bh.b_bdev before passing bh into get_block(). It is
> possible that the filesystem's get_block() will update bh.b_bdev, and this
> is fine - we just want to initialize bh.b_bdev to something reasonable so
> that the calls to __dax_dbg() work and print something useful.
>
> Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Looks good. But don't you need to do the same for __dax_fault(),
dax_zero_page_range() and similar places passing bh to dax functions?
Honza
> ---
> fs/dax.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 7af8797..513bba5 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -624,6 +624,7 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned
> long address,
> }
>
> memset(&bh, 0, sizeof(bh));
> + bh.b_bdev = inode->i_sb->s_bdev;
> block = (sector_t)pgoff << (PAGE_SHIFT - blkbits);
>
> bh.b_size = PMD_SIZE;
> --
> 2.5.0
>
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
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