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    SubjectRe: [PATCH 11/19] xfs: Convert to new freezing code
    On Fri 09-03-12 10:20:41, Dave Chinner wrote:
    > On Mon, Mar 05, 2012 at 05:01:09PM +0100, Jan Kara wrote:
    > > Generic code now blocks all writers from standard write paths. So we block all
    > > writers coming from ioctl and replace blocking of transactions on frozen
    > > filesystem with a debugging check. As a bonus, we get a protection of ioctl
    > > against racing remount read-only. We also convert xfs_file_aio_write() to a
    > > non-racy freeze protection.
    > ....
    > > diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
    > > index 329b06a..6468a2a 100644
    > > --- a/fs/xfs/xfs_trans.c
    > > +++ b/fs/xfs/xfs_trans.c
    > > @@ -577,7 +577,6 @@ 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);
    > > }
    >
    > So what is there to stop internal XFS threads from starting
    > transactions when the filesystem is frozen? Previously this
    > SB_FREEZE_TRANS would guarantee even internal fucntions would get
    > stopped, but now there's nothing?
    I've checked XFS now and I didn't find any work that would be done on a
    clean filesystem. I found:
    _xfs_mru_cache_reap() - doesn't seem to do any IO
    xfs_end_io(), xfs_buf_iodone_work() - shouldn't be a problem either since only
    reads can happen on a frozen filesystem
    xfs_reclaim_worker() - everything is clean so no IO should happen
    xfs_flush_worker() - everything is clean so no IO should happen
    xfs_sync_worker() - again the same if I understand the code right

    Honza
    --
    Jan Kara <jack@suse.cz>
    SUSE Labs, CR


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