[XFS] using a spinlock per cpu for superblock counter exclusion resul…

…ts in a preēmpt counter overflow at 256p and above. Change the exclusion mechanism to use atomic bit operations and busy wait loops to emulate the spin lock exclusion mechanism but without the preempt count issues. SGI-PV: 950027 SGI-Modid: xfs-linux-melb:xfs-kern:25338a Signed-off-by: David Chinner <dgc@sgi.com> Signed-off-by: Nathan Scott <nathans@sgi.com>
git-mirror · Mar 14, 2006 · 01e1b69 · 01e1b69
1 parent 87cbc49
commit 01e1b69
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Showing 3 changed files with 28 additions and 14 deletions.
diff --git a/fs/xfs/linux-2.6/xfs_linux.h b/fs/xfs/linux-2.6/xfs_linux.h
@@ -75,6 +75,7 @@
 #include <linux/sort.h>
 #include <linux/cpu.h>
 #include <linux/notifier.h>
+#include <linux/delay.h>
 
 #include <asm/page.h>
 #include <asm/div64.h>

diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
@@ -1746,10 +1746,7 @@ xfs_icsb_cpu_notify(
 	case CPU_UP_PREPARE:
 		/* Easy Case - initialize the area and locks, and
 		 * then rebalance when online does everything else for us. */
-		spin_lock_init(&cntp->icsb_lock);
-		cntp->icsb_icount = 0;
-		cntp->icsb_ifree = 0;
-		cntp->icsb_fdblocks = 0;
+		memset(cntp, 0, sizeof(xfs_icsb_cnts_t));
 		break;
 	case CPU_ONLINE:
 		xfs_icsb_balance_counter(mp, XFS_SBS_ICOUNT, 0);
@@ -1769,9 +1766,7 @@ xfs_icsb_cpu_notify(
 		mp->m_sb.sb_ifree += cntp->icsb_ifree;
 		mp->m_sb.sb_fdblocks += cntp->icsb_fdblocks;
 
-		cntp->icsb_icount = 0;
-		cntp->icsb_ifree = 0;
-		cntp->icsb_fdblocks = 0;
+		memset(cntp, 0, sizeof(xfs_icsb_cnts_t));
 
 		xfs_icsb_balance_counter(mp, XFS_SBS_ICOUNT, XFS_ICSB_SB_LOCKED);
 		xfs_icsb_balance_counter(mp, XFS_SBS_IFREE, XFS_ICSB_SB_LOCKED);
@@ -1800,7 +1795,7 @@ xfs_icsb_init_counters(
 
 	for_each_online_cpu(i) {
 		cntp = (xfs_icsb_cnts_t *)per_cpu_ptr(mp->m_sb_cnts, i);
-		spin_lock_init(&cntp->icsb_lock);
+		memset(cntp, 0, sizeof(xfs_icsb_cnts_t));
 	}
 	/*
 	 * start with all counters disabled so that the
@@ -1820,6 +1815,22 @@ xfs_icsb_destroy_counters(
 	}
 }
 
+STATIC inline void
+xfs_icsb_lock_cntr(
+	xfs_icsb_cnts_t	*icsbp)
+{
+	while (test_and_set_bit(XFS_ICSB_FLAG_LOCK, &icsbp->icsb_flags)) {
+		ndelay(1000);
+	}
+}
+
+STATIC inline void
+xfs_icsb_unlock_cntr(
+	xfs_icsb_cnts_t	*icsbp)
+{
+	clear_bit(XFS_ICSB_FLAG_LOCK, &icsbp->icsb_flags);
+}
+
 
 STATIC inline void
 xfs_icsb_lock_all_counters(
@@ -1830,7 +1841,7 @@ xfs_icsb_lock_all_counters(
 
 	for_each_online_cpu(i) {
 		cntp = (xfs_icsb_cnts_t *)per_cpu_ptr(mp->m_sb_cnts, i);
-		spin_lock(&cntp->icsb_lock);
+		xfs_icsb_lock_cntr(cntp);
 	}
 }
 
@@ -1843,7 +1854,7 @@ xfs_icsb_unlock_all_counters(
 
 	for_each_online_cpu(i) {
 		cntp = (xfs_icsb_cnts_t *)per_cpu_ptr(mp->m_sb_cnts, i);
-		spin_unlock(&cntp->icsb_lock);
+		xfs_icsb_unlock_cntr(cntp);
 	}
 }
 
@@ -2070,7 +2081,7 @@ xfs_icsb_modify_counters_int(
 again:
 	cpu = get_cpu();
 	icsbp = (xfs_icsb_cnts_t *)per_cpu_ptr(mp->m_sb_cnts, cpu),
-	spin_lock(&icsbp->icsb_lock);
+	xfs_icsb_lock_cntr(icsbp);
 	if (unlikely(xfs_icsb_counter_disabled(mp, field)))
 		goto slow_path;
 
@@ -2104,7 +2115,7 @@ xfs_icsb_modify_counters_int(
 		BUG();
 		break;
 	}
-	spin_unlock(&icsbp->icsb_lock);
+	xfs_icsb_unlock_cntr(icsbp);
 	put_cpu();
 	if (locked)
 		XFS_SB_UNLOCK(mp, s);
@@ -2120,7 +2131,7 @@ xfs_icsb_modify_counters_int(
 	 * manner.
 	 */
 slow_path:
-	spin_unlock(&icsbp->icsb_lock);
+	xfs_icsb_unlock_cntr(icsbp);
 	put_cpu();
 
 	/* need to hold superblock incase we need

diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
@@ -280,9 +280,11 @@ typedef struct xfs_icsb_cnts {
 	uint64_t	icsb_fdblocks;
 	uint64_t	icsb_ifree;
 	uint64_t	icsb_icount;
-	spinlock_t	icsb_lock;
+	unsigned long	icsb_flags;
 } xfs_icsb_cnts_t;
 
+#define XFS_ICSB_FLAG_LOCK	(1 << 0)	/* counter lock bit */
+
 #define XFS_ICSB_SB_LOCKED	(1 << 0)	/* sb already locked */
 #define XFS_ICSB_LAZY_COUNT	(1 << 1)	/* accuracy not needed */