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    SubjectRe: [PATCH v2] fs: Invalidate the cache for a parent block-device if fsync() is called for a partition
    On Mon, 23 Jan 2012, Niels de Vos wrote:

    > Executing an fsync() on a file-descriptor of a partition flushes the
    > caches for that partition by calling blkdev_issue_flush(). However, it
    > seems that reading data through the parent device will still return the
    > old cached data.
    >
    > The cache for the block-device is not synced if the block-device is kept
    > open (due to a mounted partition, for example). Only when all users for
    > the disk have exited, the cache for the disk is made consistent again.
    >
    > Calling invalidate_bdev() on the parent block-device in case
    > blkdev_fsync() was called for a partition, fixes this.
    >
    > The problem can be worked around by forcing the caches to be flushed
    > with either
    > # blockdev --flushbufs ${dev_disk}
    > or
    > # echo 3 > /proc/sys/vm/drop_caches
    >
    > CC: Bryn M. Reeves <bmr@redhat.com>
    > CC: Mikulas Patocka <mpatocka@redhat.com>
    > Signed-off-by: Niels de Vos <ndevos@redhat.com>
    >

    Acked-by: Mikulas Patocka <mpatocka@redhat.com>

    > ---
    > v2:
    > - Do not call invalidate_bdev() from blkdev_issue_flush() and prevent
    > performance degration with journalled filesystems.
    >
    > Suggested was to call invalidate_bdev() in fsync_bdev(), but this is
    > not in the call-path of mkfs.ext3 and similar tools. Hence the issue
    > persists.
    >
    > - Correct phrasing a little, changing ioctl-BLKFLSBUF is not required.
    >
    > - This issue also occurs when doing an ioctl-BLKFLSBUF on a partition.
    > Reading the whole disk will still return cached data. If this is an
    > issue, it will need a seperate patch.
    > ---
    > fs/block_dev.c | 4 ++++
    > 1 files changed, 4 insertions(+), 0 deletions(-)
    >
    > diff --git a/fs/block_dev.c b/fs/block_dev.c
    > index 0e575d1..433c4de 100644
    > --- a/fs/block_dev.c
    > +++ b/fs/block_dev.c
    > @@ -424,6 +424,10 @@ int blkdev_fsync(struct file *filp, loff_t start, loff_t end, int datasync)
    > if (error == -EOPNOTSUPP)
    > error = 0;
    >
    > + /* invalidate parent block_device */
    > + if (!error && bdev != bdev->bd_contains)
    > + invalidate_bdev(bdev->bd_contains);
    > +
    > return error;
    > }
    > EXPORT_SYMBOL(blkdev_fsync);
    > --
    > 1.7.6.5
    >


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