This patch makes device-mapper to use bdlookup to allow resizing
of noflush-suspended device.
With this patch, by using bdlookup() instead of bdget(),
resizing will no longer wait for I_LOCK.
There is a race between bdlookup() and bdget().
However, it's benign because the only use of bdev obtained by
bdlookup() is to modify i_size and bdget() will anyway see the
updated disk size.
(See below)
Case 1:
CPU 0 CPU 1
------------------------------------------------------------------
set_capacity()
disk size is updated
bdlookup() -> NULL
bdget()
bdget reads updated disk size
and set it to bdev inode's i_size
Case 2:
CPU 0 CPU 1
------------------------------------------------------------------
set_capacity()
disk size is updated
bdget()
bdget reads updated disk size
and set it to bdev inode's i_size
bdlookup()
wait for the bdget completion (I_NEW)
and get the bdev inode with updated disk size
Case 3:
CPU 0 CPU 1
------------------------------------------------------------------
bdget()
bdget reads old disk size
set_capacity()
disk size is updated
bdlookup()
get the existing bdev inode
update the i_size
To change i_size of bdev inode, the new code uses bd_mutex
instead of inode->i_mutex. According to a comment in
include/linux/fs.h, mutex is necessary here only to serialize
i_size_write().
bd_inode->i_size is set via bd_set_size() and bd_set_size()
is protected by bd_mutex.
So I think bd_mutex is the lock we should use.
Signed-off-by: Jun'ichi Nomura <j-nomura@xxxxxxxxxxxxx>
---
dm.c | 27 ++++++++++++++++++++++-----
1 file changed, 22 insertions(+), 5 deletions(-)
Index: linux-2.6.23.work/drivers/md/dm.c
===================================================================
--- linux-2.6.23.work.orig/drivers/md/dm.c
+++ linux-2.6.23.work/drivers/md/dm.c
@@ -1101,11 +1101,29 @@ static void event_callback(void *context
static void __set_size(struct mapped_device *md, sector_t size)
{
+ struct block_device *bdev;
+
set_capacity(md->disk, size);
- mutex_lock(&md->suspended_bdev->bd_inode->i_mutex);
- i_size_write(md->suspended_bdev->bd_inode, (loff_t)size << SECTOR_SHIFT);
- mutex_unlock(&md->suspended_bdev->bd_inode->i_mutex);
+ /*
+ * Updated disk size should be visible to bdget() possibly
+ * called in parallel to bdlookup()
+ */
+ smp_mb();
+
+ if (md->suspended_bdev)
+ bdev = md->suspended_bdev;
+ else
+ bdev = bdlookup_disk(md->disk, 0);
+
+ if (bdev) {
+ mutex_lock(&bdev->bd_mutex);
+ i_size_write(bdev->bd_inode, (loff_t)size << SECTOR_SHIFT);
+ mutex_unlock(&bdev->bd_mutex);
+ }
+
+ if (!md->suspended_bdev)
+ bdput(bdev);
}
static int __bind(struct mapped_device *md, struct dm_table *t)
@@ -1121,8 +1139,7 @@ static int __bind(struct mapped_device *
if (size != get_capacity(md->disk))
memset(&md->geometry, 0, sizeof(md->geometry));
- if (md->suspended_bdev)
- __set_size(md, size);
+ __set_size(md, size);
if (size == 0)
return 0;
--
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