dax: fix NULL pointer dereference in __dax_dbg()
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
Signed-off-by: Ross Zwisler <email@example.com>
Reported-by: Dan Williams <firstname.lastname@example.org>
Cc: Jan Kara <email@example.com>
Signed-off-by: Andrew Morton <firstname.lastname@example.org>
Signed-off-by: Linus Torvalds <email@example.com>
1 file changed