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Re: [PATCH 6/8] xfs: Use generic writers counter instead of m_active_tra

To: Jan Kara <jack@xxxxxxx>
Subject: Re: [PATCH 6/8] xfs: Use generic writers counter instead of m_active_trans counter
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Fri, 03 Feb 2012 22:34:30 -0600
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, Dave Chinner <dchinner@xxxxxxxxxx>, Surbhi Palande <csurbhi@xxxxxxxxx>, Kamal Mostafa <kamal@xxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, LKML <linux-kernel@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx
In-reply-to: <1327091686-23177-7-git-send-email-jack@xxxxxxx>
References: <1327091686-23177-1-git-send-email-jack@xxxxxxx> <1327091686-23177-7-git-send-email-jack@xxxxxxx>
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:10.0) Gecko/20120129 Thunderbird/10.0
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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