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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>