Date:	Fri, 03 Feb 2012 22:34:30 -0600
From:	Eric Sandeen <sandeen@...deen.net>
To:	Jan Kara <jack@...e.cz>
CC:	linux-fsdevel@...r.kernel.org, Dave Chinner <dchinner@...hat.com>,
	Surbhi Palande <csurbhi@...il.com>,
	Kamal Mostafa <kamal@...onical.com>,
	Christoph Hellwig <hch@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>, xfs@....sgi.com,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 6/8] xfs: Use generic writers counter instead of m_active_trans
 counter

On 1/20/12 2:34 PM, Jan Kara wrote:
> m_active_trans counter is racy wrt filesystem freezing. The patch replaces it
> with generic counter of running transactions which is properly synchronized
> with filesystem freezing. Things are a bit more complex because we need to log
> a dummy transaction and free block counters after the filesystem is frozen so
> we need to pass information to _xfs_trans_alloc() whether the transaction is
> part of filesystem freezing or not.

Here's the version I have which will get me past xfstest 068 and avoids
some warnings.

This version brings the sb_start_write go/nogo flag up to
xfs_log_sbcount() to avoid a warning at unmount time.

I'd still like to make some of the variable/macro naming more obvious
but this might do for now.

diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index 1c6fdeb..503fdfa 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -645,12 +645,13 @@ out:
  */
 int
 xfs_fs_log_dummy(
-	xfs_mount_t	*mp)
+	xfs_mount_t	*mp,
+	bool		for_freeze)
 {
 	xfs_trans_t	*tp;
 	int		error;
 
-	tp = _xfs_trans_alloc(mp, XFS_TRANS_DUMMY1, KM_SLEEP);
+	tp = _xfs_trans_alloc(mp, XFS_TRANS_DUMMY1, KM_SLEEP, for_freeze);
 	error = xfs_trans_reserve(tp, 0, mp->m_sb.sb_sectsize + 128, 0, 0,
 					XFS_DEFAULT_LOG_COUNT);
 	if (error) {
diff --git a/fs/xfs/xfs_fsops.h b/fs/xfs/xfs_fsops.h
index 1b6a98b..4d6253e 100644
--- a/fs/xfs/xfs_fsops.h
+++ b/fs/xfs/xfs_fsops.h
@@ -25,6 +25,6 @@ extern int xfs_fs_counts(xfs_mount_t *mp, xfs_fsop_counts_t *cnt);
 extern int xfs_reserve_blocks(xfs_mount_t *mp, __uint64_t *inval,
 				xfs_fsop_resblks_t *outval);
 extern int xfs_fs_goingdown(xfs_mount_t *mp, __uint32_t inflags);
-extern int xfs_fs_log_dummy(struct xfs_mount *mp);
+extern int xfs_fs_log_dummy(struct xfs_mount *mp, bool for_freeze);
 
 #endif	/* __XFS_FSOPS_H__ */
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 246c7d5..99f4e42 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -679,8 +679,8 @@ xfs_iomap_write_unwritten(
 		 * the same inode that we complete here and might deadlock
 		 * on the iolock.
 		 */
-		xfs_wait_for_freeze(mp, SB_FREEZE_TRANS);
-		tp = _xfs_trans_alloc(mp, XFS_TRANS_STRAT_WRITE, KM_NOFS);
+		tp = _xfs_trans_alloc(mp, XFS_TRANS_STRAT_WRITE,
+				KM_NOFS, XFS_HONOR_FREEZE_TRANS);
 		tp->t_flags |= XFS_TRANS_RESERVE;
 		error = xfs_trans_reserve(tp, resblks,
 				XFS_WRITE_LOG_RES(mp), 0,
diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h
index 828662f..b2731ea 100644
--- a/fs/xfs/xfs_linux.h
+++ b/fs/xfs/xfs_linux.h
@@ -308,4 +308,7 @@ static inline __uint64_t howmany_64(__uint64_t x, __uint32_t y)
 
 #endif /* DEBUG */
 
+#define XFS_HONOR_FREEZE_TRANS	false
+#define XFS_IGNORE_FREEZE_TRANS	true
+
 #endif /* __XFS_LINUX__ */
diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index d06afbc..663bc96 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -1513,7 +1513,7 @@ xfs_unmountfs(
 		xfs_warn(mp, "Unable to free reserved block pool. "
 				"Freespace may not be correct on next mount.");
 
-	error = xfs_log_sbcount(mp);
+	error = xfs_log_sbcount(mp, XFS_HONOR_FREEZE_TRANS);
 	if (error)
 		xfs_warn(mp, "Unable to update superblock counters. "
 				"Freespace may not be correct on next mount.");
@@ -1555,7 +1555,7 @@ xfs_fs_writable(xfs_mount_t *mp)
  * block when the transaction subsystem is in its frozen state.
  */
 int
-xfs_log_sbcount(xfs_mount_t *mp)
+xfs_log_sbcount(xfs_mount_t *mp, int freezing)
 {
 	xfs_trans_t	*tp;
 	int		error;
@@ -1572,7 +1572,7 @@ xfs_log_sbcount(xfs_mount_t *mp)
 	if (!xfs_sb_version_haslazysbcount(&mp->m_sb))
 		return 0;
 
-	tp = _xfs_trans_alloc(mp, XFS_TRANS_SB_COUNT, KM_SLEEP);
+	tp = _xfs_trans_alloc(mp, XFS_TRANS_SB_COUNT, KM_SLEEP, freezing);
 	error = xfs_trans_reserve(tp, 0, mp->m_sb.sb_sectsize + 128, 0, 0,
 					XFS_DEFAULT_LOG_COUNT);
 	if (error) {
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index 19f69e2..9319047 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -195,7 +195,6 @@ typedef struct xfs_mount {
 	uint			m_chsize;	/* size of next field */
 	struct xfs_chash	*m_chash;	/* fs private inode per-cluster
 						 * hash table */
-	atomic_t		m_active_trans;	/* number trans frozen */
 #ifdef HAVE_PERCPU_SB
 	xfs_icsb_cnts_t __percpu *m_sb_cnts;	/* per-cpu superblock counters */
 	unsigned long		m_icsb_counters; /* disabled per-cpu counters */
@@ -311,7 +310,6 @@ void xfs_do_force_shutdown(struct xfs_mount *mp, int flags, char *fname,
 #define SHUTDOWN_DEVICE_REQ	0x0020	/* failed all paths to the device */
 
 #define xfs_test_for_freeze(mp)		((mp)->m_super->s_frozen)
-#define xfs_wait_for_freeze(mp,l)	vfs_check_frozen((mp)->m_super, (l))
 
 /*
  * Flags for xfs_mountfs
@@ -370,7 +368,7 @@ typedef struct xfs_mod_sb {
 	int64_t		msb_delta;	/* Change to make to specified field */
 } xfs_mod_sb_t;
 
-extern int	xfs_log_sbcount(xfs_mount_t *);
+extern int	xfs_log_sbcount(xfs_mount_t *, int);
 extern __uint64_t xfs_default_resblks(xfs_mount_t *mp);
 extern int	xfs_mountfs(xfs_mount_t *mp);
 
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index ee5b695..a257077 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -1198,7 +1198,7 @@ xfs_fs_freeze(
 
 	xfs_save_resvblks(mp);
 	xfs_quiesce_attr(mp);
-	return -xfs_fs_log_dummy(mp);
+	return -xfs_fs_log_dummy(mp, XFS_IGNORE_FREEZE_TRANS);
 }
 
 STATIC int
@@ -1285,7 +1285,6 @@ xfs_fs_fill_super(
 
 	spin_lock_init(&mp->m_sb_lock);
 	mutex_init(&mp->m_growlock);
-	atomic_set(&mp->m_active_trans, 0);
 
 	mp->m_super = sb;
 	sb->s_fs_info = mp;
diff --git a/fs/xfs/xfs_sync.c b/fs/xfs/xfs_sync.c
index 40b75ee..b9a6be0 100644
--- a/fs/xfs/xfs_sync.c
+++ b/fs/xfs/xfs_sync.c
@@ -406,7 +406,7 @@ xfs_quiesce_data(
 
 	/* mark the log as covered if needed */
 	if (xfs_log_need_covered(mp))
-		error2 = xfs_fs_log_dummy(mp);
+		error2 = xfs_fs_log_dummy(mp, XFS_HONOR_FREEZE_TRANS);
 
 	/* flush data-only devices */
 	if (mp->m_rtdev_targp)
@@ -454,20 +454,13 @@ xfs_quiesce_attr(
 	int	error = 0;
 
 	/* wait for all modifications to complete */
-	while (atomic_read(&mp->m_active_trans) > 0)
-		delay(100);
+	sb_wait_write(mp->m_super, SB_FREEZE_TRANS);
 
 	/* flush inodes and push all remaining buffers out to disk */
 	xfs_quiesce_fs(mp);
 
-	/*
-	 * Just warn here till VFS can correctly support
-	 * read-only remount without racing.
-	 */
-	WARN_ON(atomic_read(&mp->m_active_trans) != 0);
-
 	/* Push the superblock and write an unmount record */
-	error = xfs_log_sbcount(mp);
+	error = xfs_log_sbcount(mp, XFS_IGNORE_FREEZE_TRANS);
 	if (error)
 		xfs_warn(mp, "xfs_attr_quiesce: failed to log sb changes. "
 				"Frozen image may not be consistent.");
@@ -500,7 +493,7 @@ xfs_sync_worker(
 		/* dgc: errors ignored here */
 		if (mp->m_super->s_frozen == SB_UNFROZEN &&
 		    xfs_log_need_covered(mp))
-			error = xfs_fs_log_dummy(mp);
+			error = xfs_fs_log_dummy(mp, XFS_HONOR_FREEZE_TRANS);
 		else
 			xfs_log_force(mp, 0);
 
diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index 329b06a..dda8877 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -577,24 +577,28 @@ xfs_trans_alloc(
 	xfs_mount_t	*mp,
 	uint		type)
 {
-	xfs_wait_for_freeze(mp, SB_FREEZE_TRANS);
-	return _xfs_trans_alloc(mp, type, KM_SLEEP);
+	return _xfs_trans_alloc(mp, type, KM_SLEEP, XFS_HONOR_FREEZE_TRANS);
 }
 
 xfs_trans_t *
 _xfs_trans_alloc(
 	xfs_mount_t	*mp,
 	uint		type,
-	uint		memflags)
+	uint		memflags,
+	bool		freezing)
 {
 	xfs_trans_t	*tp;
 
-	atomic_inc(&mp->m_active_trans);
-
+	if (!freezing)
+		sb_start_write(mp->m_super, SB_FREEZE_TRANS);
+	else
+		WARN_ON(xfs_test_for_freeze(mp) != SB_FREEZE_TRANS);
 	tp = kmem_zone_zalloc(xfs_trans_zone, memflags);
 	tp->t_magic = XFS_TRANS_MAGIC;
 	tp->t_type = type;
 	tp->t_mountp = mp;
+	if (freezing)
+		tp->t_flags |= XFS_TRANS_FREEZING;
 	INIT_LIST_HEAD(&tp->t_items);
 	INIT_LIST_HEAD(&tp->t_busy);
 	return tp;
@@ -611,7 +615,8 @@ xfs_trans_free(
 	xfs_alloc_busy_sort(&tp->t_busy);
 	xfs_alloc_busy_clear(tp->t_mountp, &tp->t_busy, false);
 
-	atomic_dec(&tp->t_mountp->m_active_trans);
+	if (!(tp->t_flags & XFS_TRANS_FREEZING))
+		sb_end_write(tp->t_mountp->m_super, SB_FREEZE_TRANS);
 	xfs_trans_free_dqinfo(tp);
 	kmem_zone_free(xfs_trans_zone, tp);
 }
@@ -654,7 +659,10 @@ xfs_trans_dup(
 
 	xfs_trans_dup_dqinfo(tp, ntp);
 
-	atomic_inc(&tp->t_mountp->m_active_trans);
+	if (tp->t_flags & XFS_TRANS_FREEZING)
+		ntp->t_flags |= XFS_TRANS_FREEZING;
+	else
+		sb_dup_write(tp->t_mountp->m_super, SB_FREEZE_TRANS);
 	return ntp;
 }
 
diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
index f611870..cae91db 100644
--- a/fs/xfs/xfs_trans.h
+++ b/fs/xfs/xfs_trans.h
@@ -179,6 +179,7 @@ struct xfs_log_item_desc {
 #define	XFS_TRANS_SYNC		0x08	/* make commit synchronous */
 #define XFS_TRANS_DQ_DIRTY	0x10	/* at least one dquot in trx dirty */
 #define XFS_TRANS_RESERVE	0x20    /* OK to use reserved data blocks */
+#define XFS_TRANS_FREEZING	0x40	/* can happen on frozen filesystem */
 
 /*
  * Values for call flags parameter.
@@ -447,7 +448,7 @@ typedef struct xfs_trans {
  * XFS transaction mechanism exported interfaces.
  */
 xfs_trans_t	*xfs_trans_alloc(struct xfs_mount *, uint);
-xfs_trans_t	*_xfs_trans_alloc(struct xfs_mount *, uint, uint);
+xfs_trans_t	*_xfs_trans_alloc(struct xfs_mount *, uint, uint, bool);
 xfs_trans_t	*xfs_trans_dup(xfs_trans_t *);
 int		xfs_trans_reserve(xfs_trans_t *, uint, uint, uint,
 				  uint, uint);



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