[Cluster-devel] [PATCH 5 of 5] Bz #248176: GFS2: invalid metadata block - REVISED

[Wendy Cheng <wcheng@redhat.com>]

Bob Peterson wrote:
> The problem was that the journal inodes, although protected by
> a glock, were not synched with the other nodes because they don't
> use the inode glock synch operations (i.e. no "glops" were defined).
> Therefore, journal recovery on a journal-recovering node were causing
> the blocks to get out of sync with the node that was actually trying
> to use that journal as it comes back up from a reboot.
>   

I don't understand this patch either. Maybe I have worked too long in 
GFS1 so please educate me on these GFS2 internals.  Comment below:
> There are two possible solutions: (1) To make the journals use the
> normal inode glock sync operations, or (2) To make the journal
> operations take effect immediately (i.e. no caching).  Although
> option 1 works, it turns out to be a lot more code.  Steve opted
> for option 2, which is much simpler and therefore less prone to
> regression errors.
>
> Regards,
>
> Bob Peterson
> --
> Signed-off-by: Bob Peterson <rpeterso@redhat.com> 
> --
> diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
> index 58c730b..f0bcaa2 100644
> --- a/fs/gfs2/ops_fstype.c
> +++ b/fs/gfs2/ops_fstype.c
> @@ -358,7 +358,7 @@ static int init_journal(struct gfs2_sbd *sdp, int undo)
>  
>  		ip = GFS2_I(sdp->sd_jdesc->jd_inode);
>  		error = gfs2_glock_nq_init(ip->i_gl, LM_ST_SHARED,
> -					   LM_FLAG_NOEXP | GL_EXACT,
> +					   LM_FLAG_NOEXP | GL_EXACT | GL_NOCACHE,
>  					   &sdp->sd_jinode_gh);
>  		if (error) {
>  			fs_err(sdp, "can't acquire journal inode glock: %d\n",
> diff --git a/fs/gfs2/recovery.c b/fs/gfs2/recovery.c
> index 5ada38c..beb6c7a 100644
> --- a/fs/gfs2/recovery.c
> +++ b/fs/gfs2/recovery.c
> @@ -469,7 +469,7 @@ int gfs2_recover_journal(struct gfs2_jdesc *jd)
>  		};
>  
>  		error = gfs2_glock_nq_init(ip->i_gl, LM_ST_SHARED,
> -					   LM_FLAG_NOEXP, &ji_gh);
> +					   LM_FLAG_NOEXP | GL_NOCACHE, &ji_gh);
>  		if (error)
>  			goto fail_gunlock_j;
>  	} else {
>
>   
This lock is requested as "SHARED" (read lock). So how does "GL_NOCACHE" 
help it to "sync" with other nodes regarding to disk blocks sharing as 
you described above ? For a normal EXCLUSIVE inode glock with nocache, 
it will force a sync (disk blocks). However, this is a read lock. So 
what is the problem this patch has solved ?

-- Wendy