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Btrfs: fix race in sync and freeze again 

I screwed this up, there is a race between checking if there is a running
transaction and actually starting a transaction in sync where we could race
with a freezer and get ourselves into trouble.  To fix this we need to make
a new join type to only do the try lock on the freeze stuff.  If it fails
we'll return EPERM and just return from sync.  This fixes a hang Liu Bo
reported when running xfstest 68 in a loop.  Thanks,

Reported-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
This commit is contained in:
Josef Bacik 2012-09-14 10:34:40 -04:00 committed by Chris Mason
parent b3ae244e71
commit 60376ce4a8
3 changed files with 18 additions and 10 deletions
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15
fs/btrfs/super.c
View File

@ -854,16 +854,13 @@ int btrfs_sync_fs(struct super_block *sb, int wait)
btrfs_wait_ordered_extents(root, 0, 0);
spin_lock(&fs_info->trans_lock);
if (!fs_info->running_transaction) {
spin_unlock(&fs_info->trans_lock);
return 0;
}
spin_unlock(&fs_info->trans_lock);
trans = btrfs_join_transaction(root);
if (IS_ERR(trans))
trans = btrfs_join_transaction_freeze(root);
if (IS_ERR(trans)) {
/* Frozen, don't bother */
if (PTR_ERR(trans) == -EPERM)
return 0;
return PTR_ERR(trans);
}
return btrfs_commit_transaction(trans, root);
}

12
fs/btrfs/transaction.c
View File

@ -272,6 +272,7 @@ enum btrfs_trans_type {
TRANS_JOIN,
TRANS_USERSPACE,
TRANS_JOIN_NOLOCK,
TRANS_JOIN_FREEZE,
};
static int may_wait_transaction(struct btrfs_root *root, int type)
@ -341,7 +342,11 @@ again:
if (!h)
return ERR_PTR(-ENOMEM);
sb_start_intwrite(root->fs_info->sb);
if (!__sb_start_write(root->fs_info->sb, SB_FREEZE_FS, false)) {
if (type == TRANS_JOIN_FREEZE)
return ERR_PTR(-EPERM);
sb_start_intwrite(root->fs_info->sb);
}
if (may_wait_transaction(root, type))
wait_current_trans(root);
@ -424,6 +429,11 @@ struct btrfs_trans_handle *btrfs_start_ioctl_transaction(struct btrfs_root *root
return start_transaction(root, 0, TRANS_USERSPACE, 0);
}
struct btrfs_trans_handle *btrfs_join_transaction_freeze(struct btrfs_root *root)
{
return start_transaction(root, 0, TRANS_JOIN_FREEZE, 0);
}
/* wait for a transaction commit to be fully complete */
static noinline void wait_for_commit(struct btrfs_root *root,
struct btrfs_transaction *commit)

1
fs/btrfs/transaction.h
View File

@ -102,6 +102,7 @@ struct btrfs_trans_handle *btrfs_start_transaction_noflush(
struct btrfs_root *root, int num_items);
struct btrfs_trans_handle *btrfs_join_transaction(struct btrfs_root *root);
struct btrfs_trans_handle *btrfs_join_transaction_nolock(struct btrfs_root *root);
struct btrfs_trans_handle *btrfs_join_transaction_freeze(struct btrfs_root *root);
struct btrfs_trans_handle *btrfs_start_ioctl_transaction(struct btrfs_root *root);
int btrfs_wait_for_commit(struct btrfs_root *root, u64 transid);
int btrfs_write_and_wait_transaction(struct btrfs_trans_handle *trans,