[Cluster-devel] Fix locking bug in failed shared to exclusive conversion

[Benjamin Marzinski <bmarzins@redhat.com>]

After calling out to the dlm, GFS2 sets the new state of a glock to
gl_target in gdlm_ast().  However, gl_target is not always the lock
state that was requested. If a conversion from shared to exclusive
fails, finish_xmote() will call do_xmote() with LM_ST_UNLOCKED, instead
of gl->gl_target, so that it can reacquire the lock in exlusive the next
time around.  In this case, setting the lock to gl_target in gdlm_ast()
will make GFS2 think that it has the glock in exclusive mode, when
really, it doesn't have the glock locked at all.  This patch adds a new
field to the gfs2_glock structure, gl_req, to track the mode that was
requested.

Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
---
 fs/gfs2/incore.h   |    1 +
 fs/gfs2/lock_dlm.c |    7 ++++---
 2 files changed, 5 insertions(+), 3 deletions(-)

Index: gfs2-2.6-nmw/fs/gfs2/incore.h
===================================================================
--- gfs2-2.6-nmw.orig/fs/gfs2/incore.h
+++ gfs2-2.6-nmw/fs/gfs2/incore.h
@@ -203,6 +203,7 @@ struct gfs2_glock {
 	unsigned int gl_target;
 	unsigned int gl_reply;
 	unsigned int gl_hash;
+	unsigned int gl_req;
 	unsigned int gl_demote_state; /* state requested by remote node */
 	unsigned long gl_demote_time; /* time of first demote request */
 	struct list_head gl_holders;
Index: gfs2-2.6-nmw/fs/gfs2/lock_dlm.c
===================================================================
--- gfs2-2.6-nmw.orig/fs/gfs2/lock_dlm.c
+++ gfs2-2.6-nmw/fs/gfs2/lock_dlm.c
@@ -46,11 +46,11 @@ static void gdlm_ast(void *arg)
 		BUG();
 	}
 
-	ret = gl->gl_target;
+	ret = gl->gl_req;
 	if (gl->gl_lksb.sb_flags & DLM_SBF_ALTMODE) {
-		if (gl->gl_target == LM_ST_SHARED)
+		if (gl->gl_req == LM_ST_SHARED)
 			ret = LM_ST_DEFERRED;
-		else if (gl->gl_target == LM_ST_DEFERRED)
+		else if (gl->gl_req == LM_ST_DEFERRED)
 			ret = LM_ST_SHARED;
 		else
 			BUG();
@@ -147,6 +147,7 @@ static unsigned int gdlm_lock(struct gfs
 	int req;
 	u32 lkf;
 
+	gl->gl_req = req_state;
 	req = make_mode(req_state);
 	lkf = make_flags(gl->gl_lksb.sb_lkid, flags, req);