direct-io: don't read inode->i_blkbits multiple times

Since directio can work on a raw block device, and the block size of the
device can change under it, we need to do the same thing that
fs/buffer.c now does: read the block size a single time, using
ACCESS_ONCE().

Reading it multiple times can get different results, which will then
confuse the code because it actually encodes the i_blksize in
relationship to the underlying logical blocksize.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/direct-io.c b/fs/direct-io.c
index f86c720..cf5b44b 100644 (file)
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -540,6 +540,7 @@ static int get_more_blocks(struct dio *dio, struct dio_submit *sdio,
        sector_t fs_endblk;     /* Into file, in filesystem-sized blocks */
        unsigned long fs_count; /* Number of filesystem-sized blocks */
        int create;
+       unsigned int i_blkbits = sdio->blkbits + sdio->blkfactor;
 
        /*
         * If there was a memory error and we've overwritten all the
@@ -554,7 +555,7 @@ static int get_more_blocks(struct dio *dio, struct dio_submit *sdio,
                fs_count = fs_endblk - fs_startblk + 1;
 
                map_bh->b_state = 0;
-               map_bh->b_size = fs_count << dio->inode->i_blkbits;
+               map_bh->b_size = fs_count << i_blkbits;
 
                /*
                 * For writes inside i_size on a DIO_SKIP_HOLES filesystem we
@@ -1053,7 +1054,8 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
        int seg;
        size_t size;
        unsigned long addr;
-       unsigned blkbits = inode->i_blkbits;
+       unsigned i_blkbits = ACCESS_ONCE(inode->i_blkbits);
+       unsigned blkbits = i_blkbits;
        unsigned blocksize_mask = (1 << blkbits) - 1;
        ssize_t retval = -EINVAL;
        loff_t end = offset;
@@ -1149,7 +1151,7 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
        dio->inode = inode;
        dio->rw = rw;
        sdio.blkbits = blkbits;
-       sdio.blkfactor = inode->i_blkbits - blkbits;
+       sdio.blkfactor = i_blkbits - blkbits;
        sdio.block_in_file = offset >> blkbits;
 
        sdio.get_block = get_block;