GFS2: Instruct DLM to avoid queue convert slowdown

This patch instructs DLM to prevent an "in place" conversion, where the
lock just stays on the granted queue, and instead forces the conversion to
the back of the convert queue. This is done on upward conversions only.
    
This is useful in cases where, for example, a lock is frequently needed in
PR on one node, but another node needs it temporarily in EX to update it.
This may happen, for example, when the rindex is being updated by gfs2_grow.
The gfs2_grow needs to have the lock in EX, but the other nodes need to
re-read it to retrieve the updates. The glock is already granted in PR on
the non-growing nodes, so this prevents them from continually re-granting
the lock in PR, and forces the EX from gfs2_grow to go through.
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/lock_dlm.c

@@ -200,10 +200,11 @@ static int make_mode(const unsigned int lmstate)
 	return -1;
 }
 
-static u32 make_flags(const u32 lkid, const unsigned int gfs_flags,
+static u32 make_flags(struct gfs2_glock *gl, const unsigned int gfs_flags,
 		      const int req)
 {
 	u32 lkf = DLM_LKF_VALBLK;
+	u32 lkid = gl->gl_lksb.sb_lkid;
 
 	if (gfs_flags & LM_FLAG_TRY)
 		lkf |= DLM_LKF_NOQUEUE;
@@ -227,8 +228,11 @@ static u32 make_flags(const u32 lkid, const unsigned int gfs_flags,
 			BUG();
 	}
 
-	if (lkid != 0) 
+	if (lkid != 0) {
 		lkf |= DLM_LKF_CONVERT;
+		if (test_bit(GLF_BLOCKING, &gl->gl_flags))
+			lkf |= DLM_LKF_QUECVT;
+	}
 
 	return lkf;
 }
@@ -250,7 +254,7 @@ static int gdlm_lock(struct gfs2_glock *gl, unsigned int req_state,
 	char strname[GDLM_STRNAME_BYTES] = "";
 
 	req = make_mode(req_state);
-	lkf = make_flags(gl->gl_lksb.sb_lkid, flags, req);
+	lkf = make_flags(gl, flags, req);
 	gfs2_glstats_inc(gl, GFS2_LKS_DCOUNT);
 	gfs2_sbstats_inc(gl, GFS2_LKS_DCOUNT);
 	if (gl->gl_lksb.sb_lkid) {