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    Subject[PATCH 6/8] xfs: Use generic writers counter instead of m_active_trans counter
    Date
    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.

    Signed-off-by: Jan Kara <jack@suse.cz>
    ---
    fs/xfs/xfs_fsops.c | 5 +++--
    fs/xfs/xfs_fsops.h | 2 +-
    fs/xfs/xfs_iomap.c | 4 ++--
    fs/xfs/xfs_mount.c | 2 +-
    fs/xfs/xfs_mount.h | 2 --
    fs/xfs/xfs_super.c | 3 +--
    fs/xfs/xfs_sync.c | 13 +++----------
    fs/xfs/xfs_trans.c | 19 ++++++++++++-------
    fs/xfs/xfs_trans.h | 3 ++-
    9 files changed, 25 insertions(+), 28 deletions(-)

    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 9afa282..fd47f6e 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, false);
    tp->t_flags |= XFS_TRANS_RESERVE;
    error = xfs_trans_reserve(tp, resblks,
    XFS_WRITE_LOG_RES(mp), 0,
    diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
    index d06afbc..74a93c9 100644
    --- a/fs/xfs/xfs_mount.c
    +++ b/fs/xfs/xfs_mount.c
    @@ -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, true);
    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 bb24dac..1317018 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 */
    @@ -312,7 +311,6 @@ 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
    diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
    index 3eca58f..2c333be 100644
    --- a/fs/xfs/xfs_super.c
    +++ b/fs/xfs/xfs_super.c
    @@ -1242,7 +1242,7 @@ xfs_fs_freeze(

    xfs_save_resvblks(mp);
    xfs_quiesce_attr(mp);
    - return -xfs_fs_log_dummy(mp);
    + return -xfs_fs_log_dummy(mp, true);
    }

    STATIC int
    @@ -1329,7 +1329,6 @@ 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 aa3dc1a..24f4d7c 100644
    --- a/fs/xfs/xfs_sync.c
    +++ b/fs/xfs/xfs_sync.c
    @@ -373,7 +373,7 @@ 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, false);

    /* flush data-only devices */
    if (mp->m_rtdev_targp)
    @@ -421,18 +421,11 @@ 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);
    if (error)
    @@ -467,7 +460,7 @@ 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, false);
    else
    xfs_log_force(mp, 0);
    error = xfs_qm_sync(mp, SYNC_TRYLOCK);
    diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
    index 1f35b2f..e97014b 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, false);
    }

    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 +659,7 @@ xfs_trans_dup(

    xfs_trans_dup_dqinfo(tp, ntp);

    - atomic_inc(&tp->t_mountp->m_active_trans);
    + 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 3ae713c..8a04d8e 100644
    --- a/fs/xfs/xfs_trans.h
    +++ b/fs/xfs/xfs_trans.h
    @@ -180,6 +180,7 @@ 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.
    @@ -448,7 +449,7 @@ 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);
    --
    1.7.1


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