Eric Sandeen wrote:
Ingo Molnar wrote:
* Srinivasa Ds <srinivasa@xxxxxxxxxx> wrote:
On debugging I found out that,"dmsetup suspend <device name>" calls
"freeze_bdev()",which locks "bd_mount_mutex" to make sure that no new
mounts happen on bdev until thaw_bdev() is called.
This "thaw_bdev()" is getting called when we resume the device
through "dmsetup resume <device-name>".
Hence we have 2 processes,one of which locks
"bd_mount_mutex"(dmsetup suspend) and Another(dmsetup resume) unlocks
it.
hm, to me this seems quite a fragile construct - even if the
mutex-debugging warning is worked around by reverting to a semaphore.
Ingo
Ingo, what do you feel is fragile about this? It seems like this is a
reasonable way to go, except that maybe a down_trylock would be good if
a 2nd process tries to freeze while it's already frozen...
Thanks,
-Eric
Ingo, As per the discussion resending the patch with down_trylock.
Signed-off-by: Srinivasa DS <srinivasa@xxxxxxxxxx>
---
fs/block_dev.c | 2 +-
fs/buffer.c | 6 ++++--
fs/super.c | 4 ++--
include/linux/fs.h | 2 +-
4 files changed, 8 insertions(+), 6 deletions(-)
Index: linux-2.6.19-rc1/fs/block_dev.c
===================================================================
--- linux-2.6.19-rc1.orig/fs/block_dev.c
+++ linux-2.6.19-rc1/fs/block_dev.c
@@ -263,7 +263,7 @@ static void init_once(void * foo, kmem_c
{
memset(bdev, 0, sizeof(*bdev));
mutex_init(&bdev->bd_mutex);
- mutex_init(&bdev->bd_mount_mutex);
+ sema_init(&bdev->bd_mount_sem, 1);
INIT_LIST_HEAD(&bdev->bd_inodes);
INIT_LIST_HEAD(&bdev->bd_list);
#ifdef CONFIG_SYSFS
Index: linux-2.6.19-rc1/fs/buffer.c
===================================================================
--- linux-2.6.19-rc1.orig/fs/buffer.c
+++ linux-2.6.19-rc1/fs/buffer.c
@@ -188,7 +188,9 @@ struct super_block *freeze_bdev(struct b
{
struct super_block *sb;
- mutex_lock(&bdev->bd_mount_mutex);
+ if (down_trylock(&bdev->bd_mount_sem))
+ return -EBUSY;
+
sb = get_super(bdev);
if (sb && !(sb->s_flags & MS_RDONLY)) {
sb->s_frozen = SB_FREEZE_WRITE;
@@ -230,7 +232,7 @@ void thaw_bdev(struct block_device *bdev
drop_super(sb);
}
- mutex_unlock(&bdev->bd_mount_mutex);
+ up(&bdev->bd_mount_sem);
}
EXPORT_SYMBOL(thaw_bdev);
Index: linux-2.6.19-rc1/fs/super.c
===================================================================
--- linux-2.6.19-rc1.orig/fs/super.c
+++ linux-2.6.19-rc1/fs/super.c
@@ -735,9 +735,9 @@ int get_sb_bdev(struct file_system_type
* will protect the lockfs code from trying to start a snapshot
* while we are mounting
*/
- mutex_lock(&bdev->bd_mount_mutex);
+ down(&bdev->bd_mount_sem);
s = sget(fs_type, test_bdev_super, set_bdev_super, bdev);
- mutex_unlock(&bdev->bd_mount_mutex);
+ up(&bdev->bd_mount_sem);
if (IS_ERR(s))
goto error_s;
Index: linux-2.6.19-rc1/include/linux/fs.h
===================================================================
--- linux-2.6.19-rc1.orig/include/linux/fs.h
+++ linux-2.6.19-rc1/include/linux/fs.h
@@ -456,7 +456,7 @@ struct block_device {
struct inode * bd_inode; /* will die */
int bd_openers;
struct mutex bd_mutex; /* open/close mutex */
- struct mutex bd_mount_mutex; /* mount mutex */
+ struct semaphore bd_mount_sem;
struct list_head bd_inodes;
void * bd_holder;
int bd_holders;
--
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