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authorFilipe Manana <fdmanana@suse.com>2014-07-31 17:41:07 +0400
committerChris Mason <clm@fb.com>2014-08-21 18:55:21 +0400
commit9c3b306e1c9e6be4be09e99a8fe2227d1005effc (patch)
tree3959abb99f9d14ae1ab26c0c2735e56504e5939b /fs/btrfs/ioctl.c
parent87fa3bb0786f37dff0b92f2c38421dd56d8902a9 (diff)
downloadlinux-9c3b306e1c9e6be4be09e99a8fe2227d1005effc.tar.xz
Btrfs: race free update of commit root for ro snapshots
This is a better solution for the problem addressed in the following commit: Btrfs: update commit root on snapshot creation after orphan cleanup (3821f348889e506efbd268cc8149e0ebfa47c4e5) The previous solution wasn't the best because of 2 reasons: 1) It added another full transaction commit, which is more expensive than just swapping the commit root with the root; 2) If a reboot happened after the first transaction commit (the one that creates the snapshot) and before the second transaction commit, then we would end up with the same problem if a send using that snapshot was requested before the first transaction commit after the reboot. This change addresses those 2 issues. The second issue is addressed by switching the commit root in the dentry lookup VFS callback, which is also called by the snapshot/subvol creation ioctl and performs orphan cleanup if needed. Like the vfs, the ioctl locks the parent inode too, preventing race issues between a dentry lookup and snapshot creation. Cc: Alex Lyakas <alex.btrfs@zadarastorage.com> Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Chris Mason <clm@fb.com>
Diffstat (limited to 'fs/btrfs/ioctl.c')
-rw-r--r--fs/btrfs/ioctl.c33
1 files changed, 0 insertions, 33 deletions
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 47aceb494d1d..845287ca59c3 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -711,39 +711,6 @@ static int create_snapshot(struct btrfs_root *root, struct inode *dir,
if (ret)
goto fail;
- ret = btrfs_orphan_cleanup(pending_snapshot->snap);
- if (ret)
- goto fail;
-
- /*
- * If orphan cleanup did remove any orphans, it means the tree was
- * modified and therefore the commit root is not the same as the
- * current root anymore. This is a problem, because send uses the
- * commit root and therefore can see inode items that don't exist
- * in the current root anymore, and for example make calls to
- * btrfs_iget, which will do tree lookups based on the current root
- * and not on the commit root. Those lookups will fail, returning a
- * -ESTALE error, and making send fail with that error. So make sure
- * a send does not see any orphans we have just removed, and that it
- * will see the same inodes regardless of whether a transaction
- * commit happened before it started (meaning that the commit root
- * will be the same as the current root) or not.
- */
- if (readonly && pending_snapshot->snap->node !=
- pending_snapshot->snap->commit_root) {
- trans = btrfs_join_transaction(pending_snapshot->snap);
- if (IS_ERR(trans) && PTR_ERR(trans) != -ENOENT) {
- ret = PTR_ERR(trans);
- goto fail;
- }
- if (!IS_ERR(trans)) {
- ret = btrfs_commit_transaction(trans,
- pending_snapshot->snap);
- if (ret)
- goto fail;
- }
- }
-
inode = btrfs_lookup_dentry(dentry->d_parent->d_inode, dentry);
if (IS_ERR(inode)) {
ret = PTR_ERR(inode);