[PATCH] Clean up dquot pincount code

[Peter Leckie <pleckie@sgi.com>]

This is a code cleanup and optimization that removes a per mount point
spinlock from the quota code and cleans up the code.

The patch changes the pincount from being an int protected by a spinlock
to an atomic_t allowing the pincount to be manipulated without holding
the spinlock.

This cleanup also protects against random wakup's of both the aild and
xfssyncd by reevaluating the pincount after been woken. Two latter patches
will address the Spurious wakeups.

Signed-off-by: Peter Leckie <pleckie@sgi.com>

Index: 2.6.x-xfs/fs/xfs/quota/xfs_dquot_item.c
===================================================================
--- 2.6.x-xfs.orig/fs/xfs/quota/xfs_dquot_item.c	2008-09-26 14:05:03.000000000 +1000
+++ 2.6.x-xfs/fs/xfs/quota/xfs_dquot_item.c	2008-09-26 14:08:27.332921018 +1000
@@ -88,25 +88,22 @@ xfs_qm_dquot_logitem_format(
 
 /*
  * Increment the pin count of the given dquot.
- * This value is protected by pinlock spinlock in the xQM structure.
  */
 STATIC void
 xfs_qm_dquot_logitem_pin(
 	xfs_dq_logitem_t *logitem)
 {
-	xfs_dquot_t *dqp;
+	xfs_dquot_t *dqp = logitem->qli_dquot;
 
-	dqp = logitem->qli_dquot;
 	ASSERT(XFS_DQ_IS_LOCKED(dqp));
-	spin_lock(&(XFS_DQ_TO_QINF(dqp)->qi_pinlock));
-	dqp->q_pincount++;
-	spin_unlock(&(XFS_DQ_TO_QINF(dqp)->qi_pinlock));
+	atomic_inc(dqp->q_pincount);
 }
 
 /*
  * Decrement the pin count of the given dquot, and wake up
  * anyone in xfs_dqwait_unpin() if the count goes to 0.	 The
- * dquot must have been previously pinned with a call to xfs_dqpin().
+ * dquot must have been previously pinned with a call to
+ * xfs_qm_dquot_logitem_pin().
  */
 /* ARGSUSED */
 STATIC void
@@ -114,16 +111,11 @@ xfs_qm_dquot_logitem_unpin(
 	xfs_dq_logitem_t *logitem,
 	int		  stale)
 {
-	xfs_dquot_t *dqp;
+	xfs_dquot_t *dqp = logitem->qli_dquot;
 
-	dqp = logitem->qli_dquot;
-	ASSERT(dqp->q_pincount > 0);
-	spin_lock(&(XFS_DQ_TO_QINF(dqp)->qi_pinlock));
-	dqp->q_pincount--;
-	if (dqp->q_pincount == 0) {
-		sv_broadcast(&dqp->q_pinwait);
-	}
-	spin_unlock(&(XFS_DQ_TO_QINF(dqp)->qi_pinlock));
+	ASSERT(atomic_read(&dqp->q_pincount) > 0);
+	if (atomic_dec_and_test(&dqp->q_pincount))
+		wake_up(&dqp->q_pinwait);
 }
 
 /* ARGSUSED */
@@ -193,21 +185,14 @@ xfs_qm_dqunpin_wait(
 	xfs_dquot_t	*dqp)
 {
 	ASSERT(XFS_DQ_IS_LOCKED(dqp));
-	if (dqp->q_pincount == 0) {
+	if (atomic_read(&dqp->q_pincount) == 0)
 		return;
-	}
 
 	/*
 	 * Give the log a push so we don't wait here too long.
 	 */
 	xfs_log_force(dqp->q_mount, (xfs_lsn_t)0, XFS_LOG_FORCE);
-	spin_lock(&(XFS_DQ_TO_QINF(dqp)->qi_pinlock));
-	if (dqp->q_pincount == 0) {
-		spin_unlock(&(XFS_DQ_TO_QINF(dqp)->qi_pinlock));
-		return;
-	}
-	sv_wait(&(dqp->q_pinwait), PINOD,
-		&(XFS_DQ_TO_QINF(dqp)->qi_pinlock), s);
+	wait_event(dqp->q_pinwait, (atomic_read(&dqp->q_pincount) == 0));
 }
 
 /*
@@ -310,7 +295,7 @@ xfs_qm_dquot_logitem_trylock(
 	uint			retval;
 
 	dqp = qip->qli_dquot;
-	if (dqp->q_pincount > 0)
+	if (atomic_read(&dqp->q_pincount) > 0)
 		return (XFS_ITEM_PINNED);
 
 	if (! xfs_qm_dqlock_nowait(dqp))
Index: 2.6.x-xfs/fs/xfs/quota/xfs_dquot.h
===================================================================
--- 2.6.x-xfs.orig/fs/xfs/quota/xfs_dquot.h	2008-09-26 14:06:40.000000000 +1000
+++ 2.6.x-xfs/fs/xfs/quota/xfs_dquot.h	2008-09-26 14:08:27.332921018 +1000
@@ -83,8 +83,8 @@ typedef struct xfs_dquot {
 	xfs_qcnt_t	 q_res_rtbcount;/* total realtime blks used+reserved */
 	mutex_t		 q_qlock;	/* quota lock */
 	struct completion q_flush;	/* flush completion queue */
-	uint		 q_pincount;	/* pin count for this dquot */
-	sv_t		 q_pinwait;	/* sync var for pinning */
+	atomic_t          q_pincount;	/* dquot pin count */
+	wait_queue_head_t q_pinwait;	/* dquot pinning wait queue */
 #ifdef XFS_DQUOT_TRACE
 	struct ktrace	*q_trace;	/* trace header structure */
 #endif
Index: 2.6.x-xfs/fs/xfs/quota/xfs_dquot.c
===================================================================
--- 2.6.x-xfs.orig/fs/xfs/quota/xfs_dquot.c	2008-09-26 14:06:31.000000000 +1000
+++ 2.6.x-xfs/fs/xfs/quota/xfs_dquot.c	2008-09-26 14:08:27.336920504 +1000
@@ -101,7 +101,7 @@ xfs_qm_dqinit(
 	if (brandnewdquot) {
 		dqp->dq_flnext = dqp->dq_flprev = dqp;
 		mutex_init(&dqp->q_qlock);
-		sv_init(&dqp->q_pinwait, SV_DEFAULT, "pdq");
+		init_waitqueue_head(&dqp->q_pinwait);
 
 		/*
 		 * Because we want to use a counting completion, complete
@@ -131,7 +131,7 @@ xfs_qm_dqinit(
 		 dqp->q_res_bcount = 0;
 		 dqp->q_res_icount = 0;
 		 dqp->q_res_rtbcount = 0;
-		 dqp->q_pincount = 0;
+		 atomic_set(&dqp->q_pincount, 0);
 		 dqp->q_hash = NULL;
 		 ASSERT(dqp->dq_flnext == dqp->dq_flprev);
 
@@ -1489,7 +1489,7 @@ xfs_qm_dqpurge(
 				"xfs_qm_dqpurge: dquot %p flush failed", dqp);
 		xfs_dqflock(dqp);
 	}
-	ASSERT(dqp->q_pincount == 0);
+	ASSERT(atomic_read(&dqp->q_pincount) == 0);
 	ASSERT(XFS_FORCED_SHUTDOWN(mp) ||
 	       !(dqp->q_logitem.qli_item.li_flags & XFS_LI_IN_AIL));
 
Index: 2.6.x-xfs/fs/xfs/quota/xfs_qm.h
===================================================================
--- 2.6.x-xfs.orig/fs/xfs/quota/xfs_qm.h	2008-09-26 14:05:03.000000000 +1000
+++ 2.6.x-xfs/fs/xfs/quota/xfs_qm.h	2008-09-26 14:08:27.336920504 +1000
@@ -106,7 +106,6 @@ typedef struct xfs_qm {
 typedef struct xfs_quotainfo {
 	xfs_inode_t	*qi_uquotaip;	 /* user quota inode */
 	xfs_inode_t	*qi_gquotaip;	 /* group quota inode */
-	spinlock_t	 qi_pinlock;	 /* dquot pinning lock */
 	xfs_dqlist_t	 qi_dqlist;	 /* all dquots in filesys */
 	int		 qi_dqreclaims;	 /* a change here indicates
 					    a removal in the dqlist */
Index: 2.6.x-xfs/fs/xfs/quota/xfs_qm.c
===================================================================
--- 2.6.x-xfs.orig/fs/xfs/quota/xfs_qm.c	2008-09-26 14:05:03.000000000 +1000
+++ 2.6.x-xfs/fs/xfs/quota/xfs_qm.c	2008-09-26 14:08:27.336920504 +1000
@@ -1137,7 +1137,6 @@ xfs_qm_init_quotainfo(
 		return error;
 	}
 
-	spin_lock_init(&qinf->qi_pinlock);
 	xfs_qm_list_init(&qinf->qi_dqlist, "mpdqlist", 0);
 	qinf->qi_dqreclaims = 0;
 
@@ -1234,7 +1233,6 @@ xfs_qm_destroy_quotainfo(
 	 */
 	xfs_qm_rele_quotafs_ref(mp);
 
-	spinlock_destroy(&qi->qi_pinlock);
 	xfs_qm_list_destroy(&qi->qi_dqlist);
 
 	if (qi->qi_uquotaip) {
Index: 2.6.x-xfs/fs/xfs/xfsidbg.c
===================================================================
--- 2.6.x-xfs.orig/fs/xfs/xfsidbg.c	2008-09-26 14:05:04.000000000 +1000
+++ 2.6.x-xfs/fs/xfs/xfsidbg.c	2008-09-26 14:08:27.340919991 +1000
@@ -6725,7 +6725,7 @@ xfsidbg_xqm_dquot(xfs_dquot_t *dqp)
 		(unsigned long long)dqp->q_res_rtbcount);
 	kdb_printf("qlock 0x%p  &q_flush 0x%p (%d) pincount 0x%x\n",
 		&dqp->q_qlock, &dqp->q_flush,
-		dqp->q_flush.done, dqp->q_pincount);
+		dqp->q_flush.done, atomic_read(&dqp->q_pincount));
 #ifdef XFS_DQUOT_TRACE
 	qprintf("dqtrace 0x%p\n", dqp->q_trace);
 #endif
@@ -6909,10 +6909,9 @@ xfsidbg_xqm_qinfo(xfs_mount_t *mp)
 		return;
 	}
 
-	kdb_printf("uqip 0x%p, gqip 0x%p, &pinlock 0x%p &dqlist 0x%p\n",
+	kdb_printf("uqip 0x%p, gqip 0x%p, &dqlist 0x%p\n",
 		mp->m_quotainfo->qi_uquotaip,
 		mp->m_quotainfo->qi_gquotaip,
-		&mp->m_quotainfo->qi_pinlock,
 		&mp->m_quotainfo->qi_dqlist);
 
 	kdb_printf("btmlimit 0x%x, itmlimit 0x%x, RTbtmlim 0x%x\n",