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>

1 files changed, 5 insertions, 3 deletions

diff --git a/fs/direct-io.c b/fs/direct-io.c
index f86c720dba0e..cf5b44b10c67 100644
--- 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;