Assume a filesystem with 4KB blocks. When a file has size 1000 bytes and
we issue direct IO read at offset 1024, blockdev_direct_IO() reads the
tail of the last block and the logic for handling short DIO reads in
dio_complete() results in a return value -24 (1000 - 1024) which
obviously confuses userspace.
Fix the problem by bailing out early once we sample i_size and can
reliably check that direct IO read starts beyond i_size.
Reported-by: Avi Kivity <avi@xxxxxxxxxxxx>
Fixes: 9fe55eea7e4b444bafc42fa0000cc2d1d2847275
CC: stable@xxxxxxxxxxxxxxx
CC: Steven Whitehouse <swhiteho@xxxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
fs/direct-io.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
Avi, this patch fixes the issue for me.
Honza
diff --git a/fs/direct-io.c b/fs/direct-io.c
index 18e7554cf94c..08094c9d8172 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -1163,6 +1163,15 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
}
}
+ /* Once we sampled i_size check for reads beyond EOF */
+ dio->i_size = i_size_read(inode);
+ if (iov_iter_rw(iter) == READ && offset >= dio->i_size) {
+ if (dio->flags & DIO_LOCKING)
+ mutex_unlock(&inode->i_mutex);
+ kmem_cache_free(dio_cache, dio);
+ goto out;
+ }
+
/*
* For file extending writes updating i_size before data writeouts
* complete can expose uninitialized blocks in dumb filesystems.
@@ -1216,7 +1225,6 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
sdio.next_block_for_io = -1;
dio->iocb = iocb;
- dio->i_size = i_size_read(inode);
spin_lock_init(&dio->bio_lock);
dio->refcount = 1;
--
2.1.4
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