Re: [Cluster-devel] [PATCH 4 of 5] Bz #248176: GFS2: invalid metadata block - REVISED

[Wendy Cheng]

Sorry ... hand and head do not coordinate well. Somehow I use "spin 
lock" but it is actually a semaphore.... Wendy
Bob Peterson wrote:
Part of the problem was that inodes were being recycled
before their buffers were flushed to the journal logs.
  
Set aside "after this patch, the problem goes away" thing ...

I haven't checked previous three patches yet so I may not have the 
overall picture ... but why adding the journal flush spin lock here 
could prevent the new inode to get re-used before its associated 
buffer are flushed to the logs ? Could you elaborate more ?

diff --git a/fs/gfs2/rgrp.c b/fs/gfs2/rgrp.c
index b93ac45..2d7f7ea 100644
--- a/fs/gfs2/rgrp.c
+++ b/fs/gfs2/rgrp.c
@@ -865,12 +865,15 @@ static struct inode *try_rgrp_unlink(struct 
gfs2_rgrpd *rgd, u64 *last_unlinked)
     struct inode *inode;
     u32 goal = 0, block;
     u64 no_addr;
+    struct gfs2_sbd *sdp = rgd->rd_sbd;
 
     for(;;) {
         if (goal >= rgd->rd_data)
             break;
+        down_write(&sdp->sd_log_flush_lock);
         block = rgblk_search(rgd, goal, GFS2_BLKST_UNLINKED,
                      GFS2_BLKST_UNLINKED);
+        up_write(&sdp->sd_log_flush_lock);
         if (block == BFITNOENT)
             break;
        
My concern is that GFS2's usage of sd_log_flush_lock has been very 
abused lately. The journal logic is gradually becoming difficult to 
understand and maintain. With this change, we move a local spin lock 
(that belongs to log.c) into another sub-component (rgrp). 
Intuitively, this is not right.

-- Wendy