Messages in this thread Patch in this message | | | From | Niels de Vos <> | Subject | [PATCH v2] fs: Invalidate the cache for a parent block-device if fsync() is called for a partition | Date | Mon, 23 Jan 2012 10:38:29 +0000 |
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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>
--- 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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