[Ocfs2-devel] [PATCH] ocfs2: llseek requires to ocfs2 inode lock for the file in SEEK_END

[Joel Becker]

On Thu, Jun 20, 2013 at 04:23:59PM +0800, shencanquan wrote:
> llseek requires ocfs2 inode lock for updating the file size in SEEK_END.
> because the file size maybe update on another node.
> if it not . after call llseek in SEEK_END. the position is old.
> 
> this bug can be reproduce the following scenario:
> at first ,we dd a test fileA,the file size is 10k.
> on NodeA:
> ---------
> 1) open the test fileA, lseek the end of file. and print the position.
> 2) close the test fileA
> 
> on NodeB:
> 1) open the test fileA, append the 5k data to test FileA.
> 2) lseek the end of file. and print the position.
> 3) close file.
> 
> at first we run the test program1 on NodeA , the result is 10k.
> and then run the test program2 on NodeB,  the result is 15k.
> at last, we run the test program1 on NodeA again, the result is 10k.
> 
> after apply this patch.  the three step result is 15k.
> 
> Signed-off-by: jensen <shencanquan at huawei.com>
> ---
>  fs/ocfs2/file.c |    9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
> index ff54014..3afd24c 100644
> --- a/fs/ocfs2/file.c
> +++ b/fs/ocfs2/file.c
> @@ -2626,7 +2626,16 @@ static loff_t ocfs2_file_llseek(struct file *file, loff_t offset, int whence)
>  	case SEEK_SET:
>  		break;
>  	case SEEK_END:
> +		/* SEEK_END requires the OCFS2 inode lock for the file
> +		 * because it references the file's size.
> +		 */
> +		ret = ocfs2_inode_lock(inode, NULL, 0);
> +		if (ret < 0) {
> +			mlog_errno(ret);
> +			goto out;
> +		}
>  		offset += inode->i_size;
> +		ocfs2_inode_unlock(inode, 0);

Why wouldn't ocfs2_rw_lock() work?  Just because we dont get the LVB
from it?

Joel

>  		break;
>  	case SEEK_CUR:
>  		if (offset == 0) {
> -- 
> 1.7.9.7
> 
> 
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