[Ocfs2-devel] [PATCH] ocfs2-1.4: fix sendfile locking

[Sunil Mushran <sunil.mushran@oracle.com>]

Acked-by: Sunil Mushran <sunil.mushran@oracle.com>

Mark Fasheh wrote:
> ocfs2_sendfile() was duplicating locking which happens later on in
> ocfs2_readpage(). The double locking would sometimes cause a lockup in nfsd,
> which uses ->sendfile() for fast read support. An easy way to see this is to
> mount an exported ocfs2 fs on a client and initiate two parallel read/write
> dd commands to the same file when there is low memory on the server.
>
> Fix ocfs2_sendfile() so that it only takes and immediately drops the cluster
> lock. This is consistent with the locking in ocfs2_file_splice_read().
>
> Signed-off-by: Mark Fasheh <mfasheh@suse.com>
>
> Index: linux/fs/ocfs2/file.c
> ===================================================================
> --- linux.orig/fs/ocfs2/file.c
> +++ linux/fs/ocfs2/file.c
> @@ -2511,15 +2511,14 @@ static ssize_t ocfs2_file_sendfile(struc
>  		mlog_errno(ret);
>  		goto bail;
>  	}
> +	ocfs2_inode_unlock(inode, 0);
>  
> -	down_read(&OCFS2_I(inode)->ip_alloc_sem);
> -
> +	/*
> +	 * This uses ->readpage, so we don't want to hold any cluster
> +	 * locks before the call.
> +	 */
>  	ret = generic_file_sendfile(in_file, ppos, count, actor, target);
>  
> -	up_read(&OCFS2_I(inode)->ip_alloc_sem);
> -
> -	ocfs2_inode_unlock(inode, 0);
> -
>  bail:
>  	mlog_exit(ret);
>  	return ret;