[XFS] Clean up dquot pincount code.

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.

SGI-PV: 986789

SGI-Modid: xfs-linux-melb:xfs-kern:32215a

Signed-off-by: Peter Leckie <pleckie@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: David Chinner <david@fromorbit.com>
Signed-off-by: Donald Douwsma <donaldd@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>

1 files changed, 11 insertions, 26 deletions

diff --git a/fs/xfs/quota/xfs_dquot_item.c b/fs/xfs/quota/xfs_dquot_item.c
index f028644caa5e..e33f8646418b 100644
--- a/fs/xfs/quota/xfs_dquot_item.c
+++ b/fs/xfs/quota/xfs_dquot_item.c
@@ -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))