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dax: never rely on bh.b_dev being set by get_block() 

Previously in DAX we assumed that calls to get_block() would set
bh.b_bdev, and we would then use that value even in error cases for
debugging.  This caused a NULL pointer dereference in __dax_dbg() which
was fixed by a previous commit, but that commit only changed the one
place where we were hitting an error.

Instead, update dax.c so that we always initialize bh.b_bdev as best we
can based on the information that DAX has.  get_block() may or may not
update to a new value, but this at least lets us get something helpful
from bh.b_bdev for error messages and not have to worry about whether it
was set by get_block() or not.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reported-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Ross Zwisler 2016-01-22 15:10:59 -08:00 committed by Linus Torvalds
parent 5eb88dca9c
commit eab95db69d
1 changed files with 3 additions and 0 deletions
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3
fs/dax.c
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@ -246,6 +246,7 @@ ssize_t dax_do_io(struct kiocb *iocb, struct inode *inode,
loff_t end = pos + iov_iter_count(iter);
memset(&bh, 0, sizeof(bh));
bh.b_bdev = inode->i_sb->s_bdev;
if ((flags & DIO_LOCKING) && iov_iter_rw(iter) == READ) {
struct address_space *mapping = inode->i_mapping;
@ -607,6 +608,7 @@ int __dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
memset(&bh, 0, sizeof(bh));
block = (sector_t)vmf->pgoff << (PAGE_SHIFT - blkbits);
bh.b_bdev = inode->i_sb->s_bdev;
bh.b_size = PAGE_SIZE;
repeat:
@ -1078,6 +1080,7 @@ int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length,
BUG_ON((offset + length) > PAGE_CACHE_SIZE);
memset(&bh, 0, sizeof(bh));
bh.b_bdev = inode->i_sb->s_bdev;
bh.b_size = PAGE_CACHE_SIZE;
err = get_block(inode, index, &bh, 0);
if (err < 0)