[PATCH] block: Invalidate the cache for a parent block-device ifblkdev_issue_flush() was called for a partition

From: Niels de Vos
Date: Thu Jan 19 2012 - 03:52:25 EST


Executing a BLKFLSBUF-ioctl on a partition flushes the caches for that
partition but 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_issue_flush() 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@xxxxxxxxxx>
Signed-off-by: Niels de Vos <ndevos@xxxxxxxxxx>
---
block/blk-flush.c | 3 +++
1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/block/blk-flush.c b/block/blk-flush.c
index 720ad60..e876f8e 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -448,6 +448,9 @@ int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,

if (!bio_flagged(bio, BIO_UPTODATE))
ret = -EIO;
+ else if (bdev != bdev->bd_contains)
+ /* invalidate parent block_device */
+ invalidate_bdev(bdev->bd_contains);

bio_put(bio);
return ret;
--
1.7.6.5

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