Messages in this thread Patch in this message | | | From | Luis Henriques <> | Subject | [PATCH 29/88] nbd: fsync and kill block device on shutdown | Date | Thu, 14 Mar 2013 10:35:22 +0000 |
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3.5.7.8 -stable review patch. If anyone has any objections, please let me know.
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From: Paolo Bonzini <pbonzini@redhat.com>
commit 3a2d63f87989e01437ba994df5f297528c353d7d upstream.
There are two problems with shutdown in the NBD driver.
1: Receiving the NBD_DISCONNECT ioctl does not sync the filesystem.
This patch adds the sync operation into __nbd_ioctl()'s NBD_DISCONNECT handler. This is useful because BLKFLSBUF is restricted to processes that have CAP_SYS_ADMIN, and the NBD client may not possess it (fsync of the block device does not sync the filesystem, either).
2: Once we clear the socket we have no guarantee that later reads will come from the same backing storage.
The patch adds calls to kill_bdev() in __nbd_ioctl()'s socket clearing code so the page cache is cleaned, lest reads that hit on the page cache will return stale data from the previously-accessible disk.
Example:
# qemu-nbd -r -c/dev/nbd0 /dev/sr0 # file -s /dev/nbd0 /dev/stdin: # UDF filesystem data (version 1.5) etc. # qemu-nbd -d /dev/nbd0 # qemu-nbd -r -c/dev/nbd0 /dev/sda # file -s /dev/nbd0 /dev/stdin: # UDF filesystem data (version 1.5) etc.
While /dev/sda has:
# file -s /dev/sda /dev/sda: x86 boot sector; etc.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Acked-by: Paul Clements <Paul.Clements@steeleye.com> Cc: Alex Bligh <alex@alex.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> [ luis: adjust context ] Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- drivers/block/nbd.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c index 3c4c225..7f25e24 100644 --- a/drivers/block/nbd.c +++ b/drivers/block/nbd.c @@ -584,12 +584,20 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd, struct request sreq; dev_info(disk_to_dev(nbd->disk), "NBD_DISCONNECT\n"); + if (!nbd->sock) + return -EINVAL; + mutex_unlock(&nbd->tx_lock); + fsync_bdev(bdev); + mutex_lock(&nbd->tx_lock); blk_rq_init(NULL, &sreq); sreq.cmd_type = REQ_TYPE_SPECIAL; nbd_cmd(&sreq) = NBD_CMD_DISC; + + /* Check again after getting mutex back. */ if (!nbd->sock) return -EINVAL; + nbd_send_req(nbd, &sreq); return 0; } @@ -603,6 +611,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd, nbd_clear_que(nbd); BUG_ON(!list_empty(&nbd->queue_head)); BUG_ON(!list_empty(&nbd->waiting_queue)); + kill_bdev(bdev); if (file) fput(file); return 0; @@ -683,6 +692,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd, nbd->file = NULL; nbd_clear_que(nbd); dev_warn(disk_to_dev(nbd->disk), "queue cleared\n"); + kill_bdev(bdev); if (file) fput(file); nbd->bytesize = 0; -- 1.8.1.2
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