From: Bob Peterson <rpeterso@redhat.com>
Subject: [PATCH][RHEL5.1][GFS2][bz276631] GFS2: operations hang after 	mount--RESEND
Date: Mon, 17 Sep 2007 08:47:31 -0500
Bugzilla: 276631
Message-Id: <1190036851.5632.34.camel@technetium.msp.redhat.com>
Changelog: [gfs2] operations hang after mount--RESEND


The problem boiled down to a race between the gdlm_init_threads()
function initializing thread1 and its setting of blist = 1.
Essentially, "if (current == ls->thread1)" was checked by the thread
before the thread creator set ls->thread1.

Since thread 1 is the only lock_dlm thread allowed to work on the
blocking queue, and since neither thread thought it was thread 1, no one
was working on the queue.  So blocking locks were never satisfied.

This patch fixes the race by starting the lock_dlm threads with
wrapper functions that select the correct blist value.
I've done more than 2000 iterations of the loop that was recreating
the failure and the problem does not occur with the patch.
--
Signed-off-by: Bob Peterson <rpeterso@redhat.com> 
--
diff -pur a/fs/gfs2/locking/dlm/thread.c b/fs/gfs2/locking/dlm/thread.c
--- a/fs/gfs2/locking/dlm/thread.c	2007-09-13 17:33:58.000000000 -0500
+++ b/fs/gfs2/locking/dlm/thread.c	2007-09-14 09:16:07.000000000 -0500
@@ -268,20 +268,16 @@ static inline int check_drop(struct gdlm
 	return 0;
 }
 
-static int gdlm_thread(void *data)
+static int gdlm_thread(void *data, int blist)
 {
 	struct gdlm_ls *ls = (struct gdlm_ls *) data;
 	struct gdlm_lock *lp = NULL;
-	int blist = 0;
 	uint8_t complete, blocking, submit, drop;
 	DECLARE_WAITQUEUE(wait, current);
 
 	/* Only thread1 is allowed to do blocking callbacks since gfs
 	   may wait for a completion callback within a blocking cb. */
 
-	if (current == ls->thread1)
-		blist = 1;
-
 	while (!kthread_should_stop()) {
 		set_current_state(TASK_INTERRUPTIBLE);
 		add_wait_queue(&ls->thread_wait, &wait);
@@ -333,12 +329,22 @@ static int gdlm_thread(void *data)
 	return 0;
 }
 
+static int gdlm_thread1(void *data)
+{
+	return gdlm_thread(data, 1);
+}
+
+static int gdlm_thread2(void *data)
+{
+	return gdlm_thread(data, 0);
+}
+
 int gdlm_init_threads(struct gdlm_ls *ls)
 {
 	struct task_struct *p;
 	int error;
 
-	p = kthread_run(gdlm_thread, ls, "lock_dlm1");
+	p = kthread_run(gdlm_thread1, ls, "lock_dlm1");
 	error = IS_ERR(p);
 	if (error) {
 		log_error("can't start lock_dlm1 thread %d", error);
@@ -346,7 +352,7 @@ int gdlm_init_threads(struct gdlm_ls *ls
 	}
 	ls->thread1 = p;
 
-	p = kthread_run(gdlm_thread, ls, "lock_dlm2");
+	p = kthread_run(gdlm_thread2, ls, "lock_dlm2");
 	error = IS_ERR(p);
 	if (error) {
 		log_error("can't start lock_dlm2 thread %d", error);