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direct-io: Fix negative return from dio read beyond eof 

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@scylladb.com>
Fixes: 9fe55eea7e
CC: stable@vger.kernel.org
CC: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Jan Kara 2015-11-30 10:15:42 -07:00 committed by Jens Axboe
parent bf4e6b4e75
commit 74cedf9b6c
1 changed files with 9 additions and 1 deletions
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10
fs/direct-io.c
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@ -1169,6 +1169,15 @@ 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 * For file extending writes updating i_size before data writeouts
* complete can expose uninitialized blocks in dumb filesystems. * complete can expose uninitialized blocks in dumb filesystems.
@ -1222,7 +1231,6 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
sdio.next_block_for_io = -1; sdio.next_block_for_io = -1;
dio->iocb = iocb; dio->iocb = iocb;
dio->i_size = i_size_read(inode);
spin_lock_init(&dio->bio_lock); spin_lock_init(&dio->bio_lock);
dio->refcount = 1; dio->refcount = 1;