[Cluster-devel] [PATCH] dlm: fix basts for granted PR waiting CW -v2

[David Teigland <teigland@redhat.com>]

Fix a long standing bug where a blocking callback would be missed
when there's a granted lock in PR mode and waiting locks in both
PR and CW modes (and the PR lock was added to the waiting queue
before the CW lock).  The logic simply compared the numerical values
of the modes to determine if a blocking callback was required, but in
the one case of PR and CW, the lower valued CW mode blocks the higher
valued PR mode.  We just need to add a special check for this PR/CW
case in the tests that decide when a blocking callback is needed.

The first version of this patch would sometimes send an incorrect bast
mode of PR when it should have been CW.

Signed-off-by: David Teigland <teigland@redhat.com>

Index: linux-quilt/fs/dlm/lock.c
===================================================================
--- linux-quilt.orig/fs/dlm/lock.c
+++ linux-quilt/fs/dlm/lock.c
@@ -1670,9 +1670,10 @@ static int can_be_granted(struct dlm_rsb
    with a deadlk here, we'd have to generate something like grant_lock with
    the deadlk error.) */
 
-/* returns the highest requested mode of all blocked conversions */
+/* Returns the highest requested mode of all blocked conversions; sets
+   cw if there's a blocked conversion to DLM_LOCK_CW. */
 
-static int grant_pending_convert(struct dlm_rsb *r, int high)
+static int grant_pending_convert(struct dlm_rsb *r, int high, int *cw)
 {
 	struct dlm_lkb *lkb, *s;
 	int hi, demoted, quit, grant_restart, demote_restart;
@@ -1709,6 +1710,9 @@ static int grant_pending_convert(struct 
 		}
 
 		hi = max_t(int, lkb->lkb_rqmode, hi);
+
+		if (cw && lkb->lkb_rqmode == DLM_LOCK_CW)
+			*cw = 1;
 	}
 
 	if (grant_restart)
@@ -1721,29 +1725,52 @@ static int grant_pending_convert(struct 
 	return max_t(int, high, hi);
 }
 
-static int grant_pending_wait(struct dlm_rsb *r, int high)
+static int grant_pending_wait(struct dlm_rsb *r, int high, int *cw)
 {
 	struct dlm_lkb *lkb, *s;
 
 	list_for_each_entry_safe(lkb, s, &r->res_waitqueue, lkb_statequeue) {
 		if (can_be_granted(r, lkb, 0, NULL))
 			grant_lock_pending(r, lkb);
-                else
+                else {
 			high = max_t(int, lkb->lkb_rqmode, high);
+			if (lkb->lkb_rqmode == DLM_LOCK_CW)
+				*cw = 1;
+		}
 	}
 
 	return high;
 }
 
+/* cw of 1 means there's a lock with a rqmode of DLM_LOCK_CW that's blocked
+   on either the convert or waiting queue.
+   high is the largest rqmode of all locks blocked on the convert or
+   waiting queue. */
+
+static int lock_requires_bast(struct dlm_lkb *gr, int high, int cw)
+{
+	if (gr->lkb_grmode == DLM_LOCK_PR && cw) {
+		if (gr->lkb_highbast < DLM_LOCK_EX)
+			return 1;
+		return 0;
+	}
+
+	if (gr->lkb_highbast < high &&
+	    !__dlm_compat_matrix[gr->lkb_grmode+1][high+1])
+		return 1;
+	return 0;
+}
+
 static void grant_pending_locks(struct dlm_rsb *r)
 {
 	struct dlm_lkb *lkb, *s;
 	int high = DLM_LOCK_IV;
+	int cw = 0;
 
 	DLM_ASSERT(is_master(r), dlm_dump_rsb(r););
 
-	high = grant_pending_convert(r, high);
-	high = grant_pending_wait(r, high);
+	high = grant_pending_convert(r, high, &cw);
+	high = grant_pending_wait(r, high, &cw);
 
 	if (high == DLM_LOCK_IV)
 		return;
@@ -1751,27 +1778,41 @@ static void grant_pending_locks(struct d
 	/*
 	 * If there are locks left on the wait/convert queue then send blocking
 	 * ASTs to granted locks based on the largest requested mode (high)
-	 * found above. FIXME: highbast < high comparison not valid for PR/CW.
+	 * found above.
 	 */
 
 	list_for_each_entry_safe(lkb, s, &r->res_grantqueue, lkb_statequeue) {
-		if (lkb->lkb_bastaddr && (lkb->lkb_highbast < high) &&
-		    !__dlm_compat_matrix[lkb->lkb_grmode+1][high+1]) {
-			queue_bast(r, lkb, high);
+		if (lkb->lkb_bastaddr && lock_requires_bast(lkb, high, cw)) {
+			if (cw && high == DLM_LOCK_PR)
+				queue_bast(r, lkb, DLM_LOCK_CW);
+			else
+				queue_bast(r, lkb, high);
 			lkb->lkb_highbast = high;
 		}
 	}
 }
 
+static int modes_require_bast(struct dlm_lkb *gr, struct dlm_lkb *rq)
+{
+	if ((gr->lkb_grmode == DLM_LOCK_PR && rq->lkb_rqmode == DLM_LOCK_CW) ||
+	    (gr->lkb_grmode == DLM_LOCK_CW && rq->lkb_rqmode == DLM_LOCK_PR)) {
+		if (gr->lkb_highbast < DLM_LOCK_EX)
+			return 1;
+		return 0;
+	}
+
+	if (gr->lkb_highbast < rq->lkb_rqmode && !modes_compat(gr, rq))
+		return 1;
+	return 0;
+}
+
 static void send_bast_queue(struct dlm_rsb *r, struct list_head *head,
 			    struct dlm_lkb *lkb)
 {
 	struct dlm_lkb *gr;
 
 	list_for_each_entry(gr, head, lkb_statequeue) {
-		if (gr->lkb_bastaddr &&
-		    gr->lkb_highbast < lkb->lkb_rqmode &&
-		    !modes_compat(gr, lkb)) {
+		if (gr->lkb_bastaddr && modes_require_bast(gr, lkb)) {
 			queue_bast(r, gr, lkb->lkb_rqmode);
 			gr->lkb_highbast = lkb->lkb_rqmode;
 		}
@@ -2235,7 +2276,7 @@ static int do_convert(struct dlm_rsb *r,
 	   before we try again to grant this one. */
 
 	if (is_demoted(lkb)) {
-		grant_pending_convert(r, DLM_LOCK_IV);
+		grant_pending_convert(r, DLM_LOCK_IV, NULL);
 		if (_can_be_granted(r, lkb, 1)) {
 			grant_lock(r, lkb);
 			queue_cast(r, lkb, 0);