[Cluster-devel] [GFS2 PATCH v2] GFS2: Use local iopen glock holder in gfs2_evict_inode

[Bob Peterson]

Self-NACK. While this patch seems to fix the problem, in theory
it should not be necessary because the i_iopen_gh that may be used
by other processes should be unique to I_NEW inode. So I still have
some investigating to do here. Sorry for the noise.

Bob Peterson
Red Hat File Systems
----- Original Message -----
| Hi,
| 
| I found a couple problems with the previous version of this patch
| during testing. Here is my replacement, version 2.
| 
| Patch description:
| 
| Before this patch, function gfs2_evict_inode unlocked the iopen
| glock (from SH), waited for completion, then locked it again in
| EXclusive mode. That's all well and good except that other processes
| (not in gfs2_evict_inode) can try to do lookups, and function
| gfs2_inode_lookup tries to lock the iopen glock in SH again. This
| second lookup can and does wipe out the holder's pid with getpid().
| The first putpid (from glock_holder_uninit) will be successful, but
| the second one will crash the kernel with:
| BUG: unable to handle kernel paging request
| This patch introduces a holder variable, io_gh, local to function
| gfs2_evict_inode, which will keep its own getpid() and subsequent
| putpid() from interfering with one another. So simultaneous inode
| lookups won't change the value out from under gfs2_evict_inode.
| 
| Signed-off-by: Bob Peterson <rpeterso at redhat.com>
| ---
|  fs/gfs2/super.c | 25 ++++++++++++++++---------
|  1 file changed, 16 insertions(+), 9 deletions(-)
| 
| diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
| index 9b2ff353..21a8ba8 100644
| --- a/fs/gfs2/super.c
| +++ b/fs/gfs2/super.c
| @@ -1518,7 +1518,7 @@ static void gfs2_evict_inode(struct inode *inode)
|  	struct super_block *sb = inode->i_sb;
|  	struct gfs2_sbd *sdp = sb->s_fs_info;
|  	struct gfs2_inode *ip = GFS2_I(inode);
| -	struct gfs2_holder gh;
| +	struct gfs2_holder gh, iopen_gh;
|  	struct address_space *metamapping;
|  	int error;
|  
| @@ -1527,6 +1527,7 @@ static void gfs2_evict_inode(struct inode *inode)
|  		return;
|  	}
|  
| +	memset(&iopen_gh, 0, sizeof(iopen_gh));
|  	if (inode->i_nlink || (sb->s_flags & MS_RDONLY))
|  		goto out;
|  
| @@ -1555,9 +1556,15 @@ static void gfs2_evict_inode(struct inode *inode)
|  	    test_bit(HIF_HOLDER, &ip->i_iopen_gh.gh_iflags)) {
|  		ip->i_iopen_gh.gh_flags |= GL_NOCACHE;
|  		gfs2_glock_dq_wait(&ip->i_iopen_gh);
| -		gfs2_holder_reinit(LM_ST_EXCLUSIVE, LM_FLAG_TRY_1CB | GL_NOCACHE,
| -				   &ip->i_iopen_gh);
| -		error = gfs2_glock_nq(&ip->i_iopen_gh);
| +		/* This is subtle: Now we need to uninit the i_iopen_holder,
| +		   but if we do that before we obtain the new reference with
| +		   the local holder, the uninit's glock_put will free the
| +		   glock, which causes the new ref. to crash. So we need to do
| +		   this in a very specific order. Can't use glock_nq_init. */
| +		gfs2_holder_init(ip->i_iopen_gh.gh_gl, LM_ST_EXCLUSIVE,
| +				 LM_FLAG_TRY_1CB | GL_NOCACHE, &iopen_gh);
| +		gfs2_holder_uninit(&ip->i_iopen_gh);
| +		error = gfs2_glock_nq(&iopen_gh);
|  		if (error)
|  			goto out_truncate;
|  	}
| @@ -1610,12 +1617,12 @@ out_unlock:
|  	if (gfs2_rs_active(&ip->i_res))
|  		gfs2_rs_deltree(&ip->i_res);
|  
| -	if (ip->i_iopen_gh.gh_gl) {
| -		if (test_bit(HIF_HOLDER, &ip->i_iopen_gh.gh_iflags)) {
| -			ip->i_iopen_gh.gh_flags |= GL_NOCACHE;
| -			gfs2_glock_dq_wait(&ip->i_iopen_gh);
| +	if (iopen_gh.gh_gl) {
| +		if (test_bit(HIF_HOLDER, &iopen_gh.gh_iflags)) {
| +			iopen_gh.gh_flags |= GL_NOCACHE;
| +			gfs2_glock_dq_wait(&iopen_gh);
|  		}
| -		gfs2_holder_uninit(&ip->i_iopen_gh);
| +		gfs2_holder_uninit(&iopen_gh);
|  	}
|  	gfs2_glock_dq_uninit(&gh);
|  	if (error && error != GLR_TRYFAILED && error != -EROFS)
| 
|